diff --git a/web/kanban.go b/web/kanban.go
new file mode 100644
index 0000000..a0493e7
--- /dev/null
+++ b/web/kanban.go
@@ -0,0 +1,217 @@
+package web
+
+import (
+	"net/url"
+	"sort"
+	"strings"
+
+	"github.com/m/projax/store"
+)
+
+// Phase 5i Slice C — kanban view_type. Read-only: groups the filtered item
+// set into columns by the chosen group_by dimension. Drag-to-change-group
+// is deliberately out of scope (design.md §3 / slice ordering A→B→D→C→E).
+//
+// m's Q6 pick (2026-05-26): default group_by = status (active/done/archived).
+// Other values (area / tag / management) remain selectable via the
+// group_by chip strip.
+
+// Kanban group_by values. The DB CHECK constraint on projax.views.group_by
+// is open-ended (text); the validation list lives here so the handler can
+// reject typos before they round-trip.
+const (
+	GroupByStatus     = "status"
+	GroupByArea       = "area"
+	GroupByTag        = "tag"
+	GroupByManagement = "management"
+)
+
+var allGroupBy = []string{GroupByStatus, GroupByArea, GroupByTag, GroupByManagement}
+
+// ParseGroupBy pulls `group_by` from q. Empty / unknown values fall back to
+// the default (status). Lower-cases for case-insensitive matching.
+func ParseGroupBy(q url.Values) string {
+	raw := strings.ToLower(strings.TrimSpace(q.Get("group_by")))
+	for _, g := range allGroupBy {
+		if raw == g {
+			return g
+		}
+	}
+	return GroupByStatus
+}
+
+// KanbanColumn is one column in the rendered board.
+type KanbanColumn struct {
+	Key   string        // the raw group value (status="active", tag="work", …)
+	Label string        // human-readable header
+	Items []*store.Item // sorted: pinned-first, then updated_at desc, then title
+}
+
+// KanbanBoard is the rendered shape. Columns are ordered by the canonical
+// per-dimension order (status: active/done/archived; management: mai/self/
+// external/unmanaged; area + tag: alphabetical with the items they hold).
+type KanbanBoard struct {
+	GroupBy string
+	Columns []KanbanColumn
+	Total   int // total cards across columns
+}
+
+// BuildKanbanBoard groups the matched items by groupBy. Pure: takes whatever
+// list of items the handler filtered, returns the column shape.
+func BuildKanbanBoard(items []*store.Item, groupBy string) KanbanBoard {
+	if groupBy == "" {
+		groupBy = GroupByStatus
+	}
+	keyer := groupByKeyer(groupBy)
+	byKey := map[string][]*store.Item{}
+	emittedKeys := []string{}
+	seen := map[string]bool{}
+	for _, it := range items {
+		for _, k := range keyer(it) {
+			if !seen[k] {
+				seen[k] = true
+				emittedKeys = append(emittedKeys, k)
+			}
+			byKey[k] = append(byKey[k], it)
+		}
+	}
+	// Stable column ordering per dimension.
+	switch groupBy {
+	case GroupByStatus:
+		emittedKeys = orderKeyedFirst(emittedKeys, []string{"active", "done", "archived"})
+	case GroupByManagement:
+		emittedKeys = orderKeyedFirst(emittedKeys, []string{"mai", "self", "external", "unmanaged"})
+	default:
+		sort.Strings(emittedKeys)
+	}
+	board := KanbanBoard{GroupBy: groupBy}
+	for _, k := range emittedKeys {
+		cardItems := byKey[k]
+		sort.SliceStable(cardItems, func(i, j int) bool {
+			a, b := cardItems[i], cardItems[j]
+			if a.Pinned != b.Pinned {
+				return a.Pinned
+			}
+			if !a.UpdatedAt.Equal(b.UpdatedAt) {
+				return a.UpdatedAt.After(b.UpdatedAt)
+			}
+			return a.Title < b.Title
+		})
+		board.Columns = append(board.Columns, KanbanColumn{
+			Key:   k,
+			Label: columnLabel(groupBy, k),
+			Items: cardItems,
+		})
+		board.Total += len(cardItems)
+	}
+	return board
+}
+
+// groupByKeyer returns a function that maps an item to its column keys (a
+// slice because tags can put one item in multiple columns).
+func groupByKeyer(groupBy string) func(*store.Item) []string {
+	switch groupBy {
+	case GroupByStatus:
+		return func(it *store.Item) []string {
+			s := it.Status
+			if s == "" {
+				s = "active"
+			}
+			return []string{s}
+		}
+	case GroupByManagement:
+		return func(it *store.Item) []string {
+			if len(it.Management) == 0 {
+				return []string{"unmanaged"}
+			}
+			out := make([]string, 0, len(it.Management))
+			out = append(out, it.Management...)
+			return out
+		}
+	case GroupByArea:
+		return func(it *store.Item) []string {
+			// First segment of the primary path is the area (dev / work / home …).
+			p := it.PrimaryPath()
+			if p == "" {
+				return []string{"—"}
+			}
+			if idx := strings.IndexByte(p, '.'); idx > 0 {
+				return []string{p[:idx]}
+			}
+			return []string{p}
+		}
+	case GroupByTag:
+		return func(it *store.Item) []string {
+			if len(it.Tags) == 0 {
+				return []string{"untagged"}
+			}
+			return append([]string(nil), it.Tags...)
+		}
+	}
+	return func(it *store.Item) []string { return []string{it.Status} }
+}
+
+// columnLabel renders the column header. Status / management get title-case
+// for legibility; area and tag stay verbatim.
+func columnLabel(groupBy, key string) string {
+	switch groupBy {
+	case GroupByStatus, GroupByManagement:
+		if key == "" {
+			return "—"
+		}
+		return strings.ToUpper(key[:1]) + key[1:]
+	}
+	return key
+}
+
+// orderKeyedFirst returns `actual` with `preferred` entries first (in the
+// preferred order, when present in actual), then any remaining actual
+// entries appended in input order.
+func orderKeyedFirst(actual, preferred []string) []string {
+	present := map[string]bool{}
+	for _, k := range actual {
+		present[k] = true
+	}
+	out := make([]string, 0, len(actual))
+	for _, k := range preferred {
+		if present[k] {
+			out = append(out, k)
+			delete(present, k)
+		}
+	}
+	for _, k := range actual {
+		if present[k] {
+			out = append(out, k)
+			delete(present, k)
+		}
+	}
+	return out
+}
+
+// GroupByChip is one entry in the group-by chip strip rendered above the
+// kanban board. Active marks the current group_by; URL is the toggle target.
+type GroupByChip struct {
+	Label  string
+	URL    string
+	Active bool
+}
+
+// GroupByChips builds the group-by chip strip. base must already include the
+// `?view_type=kanban` segment; we append `&group_by=<value>` on top.
+func GroupByChips(base string, filter TreeFilter, current string) []GroupByChip {
+	out := make([]GroupByChip, 0, len(allGroupBy))
+	for _, g := range allGroupBy {
+		u := filter.URLOn(base)
+		if !strings.Contains(u, "?") {
+			u += "?view_type=kanban&group_by=" + g
+		} else {
+			u += "&view_type=kanban&group_by=" + g
+		}
+		out = append(out, GroupByChip{
+			Label:  g,
+			URL:    u,
+			Active: g == current,
+		})
+	}
+	return out
+}
diff --git a/web/kanban_test.go b/web/kanban_test.go
new file mode 100644
index 0000000..bba1f3a
--- /dev/null
+++ b/web/kanban_test.go
@@ -0,0 +1,105 @@
+package web
+
+import (
+	"net/url"
+	"testing"
+	"time"
+
+	"github.com/m/projax/store"
+)
+
+// TestBuildKanbanBoardGroupByStatus exercises the default group_by — three
+// columns in canonical order (active/done/archived) populated by status.
+func TestBuildKanbanBoardGroupByStatus(t *testing.T) {
+	items := []*store.Item{
+		{ID: "a", Title: "Active1", Status: "active", Paths: []string{"dev.a"}, UpdatedAt: time.Unix(2, 0)},
+		{ID: "b", Title: "Active2", Status: "active", Paths: []string{"dev.b"}, UpdatedAt: time.Unix(3, 0), Pinned: true},
+		{ID: "c", Title: "Done1", Status: "done", Paths: []string{"dev.c"}, UpdatedAt: time.Unix(1, 0)},
+	}
+	board := BuildKanbanBoard(items, GroupByStatus)
+	if got, want := len(board.Columns), 2; got != want {
+		t.Fatalf("columns = %d, want %d", got, want)
+	}
+	if board.Columns[0].Key != "active" {
+		t.Errorf("first column = %q, want active", board.Columns[0].Key)
+	}
+	if board.Columns[1].Key != "done" {
+		t.Errorf("second column = %q, want done", board.Columns[1].Key)
+	}
+	if board.Total != 3 {
+		t.Errorf("Total = %d, want 3", board.Total)
+	}
+	// active column: pinned-first (b), then updated_at desc (a).
+	if board.Columns[0].Items[0].ID != "b" {
+		t.Errorf("pinned item should be first; got %q", board.Columns[0].Items[0].ID)
+	}
+	if board.Columns[0].Items[1].ID != "a" {
+		t.Errorf("second active item = %q, want a", board.Columns[0].Items[1].ID)
+	}
+}
+
+// TestBuildKanbanBoardGroupByTag puts an item with multiple tags into multiple
+// columns. Columns sort alphabetically (no canonical preference for tags).
+func TestBuildKanbanBoardGroupByTag(t *testing.T) {
+	items := []*store.Item{
+		{ID: "a", Title: "A", Status: "active", Paths: []string{"a"}, Tags: []string{"work", "dev"}},
+		{ID: "b", Title: "B", Status: "active", Paths: []string{"b"}, Tags: []string{"dev"}},
+		{ID: "c", Title: "C", Status: "active", Paths: []string{"c"}, Tags: []string{}},
+	}
+	board := BuildKanbanBoard(items, GroupByTag)
+	keys := map[string]int{}
+	for _, col := range board.Columns {
+		keys[col.Key] = len(col.Items)
+	}
+	if keys["dev"] != 2 {
+		t.Errorf("dev column items = %d, want 2", keys["dev"])
+	}
+	if keys["work"] != 1 {
+		t.Errorf("work column items = %d, want 1", keys["work"])
+	}
+	if keys["untagged"] != 1 {
+		t.Errorf("untagged column items = %d, want 1", keys["untagged"])
+	}
+}
+
+// TestBuildKanbanBoardGroupByArea uses the first path segment as the area.
+func TestBuildKanbanBoardGroupByArea(t *testing.T) {
+	items := []*store.Item{
+		{ID: "a", Title: "A", Status: "active", Paths: []string{"dev.a"}},
+		{ID: "b", Title: "B", Status: "active", Paths: []string{"work.upc.b"}},
+		{ID: "c", Title: "C", Status: "active", Paths: []string{"work.c"}},
+	}
+	board := BuildKanbanBoard(items, GroupByArea)
+	keys := map[string]int{}
+	for _, col := range board.Columns {
+		keys[col.Key] = len(col.Items)
+	}
+	if keys["dev"] != 1 {
+		t.Errorf("dev column = %d, want 1", keys["dev"])
+	}
+	if keys["work"] != 2 {
+		t.Errorf("work column = %d, want 2", keys["work"])
+	}
+}
+
+// TestParseGroupByFallsBackOnUnknown verifies the parser's defaulting.
+func TestParseGroupByFallsBackOnUnknown(t *testing.T) {
+	cases := map[string]string{
+		"":              GroupByStatus,
+		"status":        GroupByStatus,
+		"tag":           GroupByTag,
+		"area":          GroupByArea,
+		"management":    GroupByManagement,
+		"MaNaGeMeNt":    GroupByManagement,
+		"made-up":       GroupByStatus,
+	}
+	for raw, want := range cases {
+		q := url.Values{}
+		if raw != "" {
+			q.Set("group_by", raw)
+		}
+		if got := ParseGroupBy(q); got != want {
+			t.Errorf("ParseGroupBy(%q) = %q, want %q", raw, got, want)
+		}
+	}
+}
diff --git a/web/server.go b/web/server.go
index e4e0783..26eab01 100644
--- a/web/server.go
+++ b/web/server.go
@@ -170,6 +170,7 @@ func New(s *store.Store, logger *slog.Logger) (*Server, error) {
 		"templates/tree.tmpl",
 		"templates/tree_section.tmpl",
 		"templates/tree_card.tmpl",
+		"templates/tree_kanban.tmpl",
 		"templates/project_chip.tmpl",
 	)
 	if err != nil {
@@ -180,6 +181,7 @@ func New(s *store.Store, logger *slog.Logger) (*Server, error) {
 	treeSection, err := template.New("tree_section").Funcs(funcs).ParseFS(templatesFS,
 		"templates/tree_section.tmpl",
 		"templates/tree_card.tmpl",
+		"templates/tree_kanban.tmpl",
 		"templates/project_chip.tmpl",
 	)
 	if err != nil {
@@ -467,6 +469,10 @@ func (s *Server) handleTree(w http.ResponseWriter, r *http.Request) {
 	// (no tree structure). Build from items + filter directly rather than
 	// reusing the post-prune `roots` (which still keeps ancestors).
 	cardItems := flatMatchedItems(items, filter, linkKinds)
+	// Phase 5i Slice C: kanban groups the same matched set into columns.
+	groupBy := ParseGroupBy(r.URL.Query())
+	kanban := BuildKanbanBoard(cardItems, groupBy)
+	groupByChips := GroupByChips("/", filter, groupBy)
 	data := map[string]any{
 		"Title":             "tree",
 		"Roots":             roots,
@@ -483,6 +489,9 @@ func (s *Server) handleTree(w http.ResponseWriter, r *http.Request) {
 		"ViewType":          view,
 		"ViewTypeChips":     ViewTypeChips("/", filter, view),
 		"CardItems":         cardItems,
+		"Kanban":            kanban,
+		"GroupBy":           groupBy,
+		"GroupByChips":      groupByChips,
 		// ActiveTags kept for backwards-compat with the old template path; removed
 		// after the template migrates fully.
 		"ActiveTags": filter.Tags,
diff --git a/web/server_test.go b/web/server_test.go
index b7c8b85..828bdfc 100644
--- a/web/server_test.go
+++ b/web/server_test.go
@@ -295,6 +295,25 @@ func TestMultiParentBothPathsRouteToSameRow(t *testing.T) {
 	}
 }
 
+// TestTreeRendersKanbanWhenViewTypeIsKanban verifies the Phase 5i Slice C
+// dispatch: GET /?view_type=kanban renders the kanban board (with the
+// group-by chip strip) instead of the forest. group_by defaults to status.
+func TestTreeRendersKanbanWhenViewTypeIsKanban(t *testing.T) {
+	srv, pool := mustServer(t)
+	defer pool.Close()
+	h := srv.Routes()
+	_, body := get(t, h, "/?view_type=kanban")
+	if !strings.Contains(body, `class="kanban-board"`) {
+		t.Error("?view_type=kanban should render the kanban board")
+	}
+	if !strings.Contains(body, `class="groupby-chip`) {
+		t.Error("kanban view should render the group-by chip strip")
+	}
+	if strings.Contains(body, `<ul class="forest">`) {
+		t.Error("kanban view should not render the tree forest")
+	}
+}
+
 // TestTreeRendersCardGridWhenViewTypeIsCard verifies Phase 5i Slice B
 // dispatch: `?view_type=card` renders the flat tile grid instead of the
 // forest, and the view-type chip strip is present in either view. Unknown
diff --git a/web/static/style.css b/web/static/style.css
index 10cb8df..3d77a57 100644
--- a/web/static/style.css
+++ b/web/static/style.css
@@ -229,6 +229,36 @@ table.classify input, table.classify select { width: 100%; }
 .tree-card-slug { font-size: 0.78em; }
 .tree-card-meta { display: flex; flex-wrap: wrap; gap: 4px; margin: 0; font-size: 0.78em; }
 .tree-card-empty { grid-column: 1 / -1; padding: 24px; color: var(--muted); }
+/* Phase 5i Slice C — kanban columns + cards. */
+.kanban-controls { margin: 8px 0; }
+.groupby-chip {
+  display: inline-block; font-size: 0.78em; padding: 1px 8px; border-radius: 999px;
+  background: var(--surface); border: 1px solid var(--border); color: var(--muted); text-decoration: none;
+}
+.groupby-chip:hover { color: var(--fg); border-color: var(--accent); }
+.kanban-board {
+  display: grid; gap: 12px; padding: 12px 0; overflow-x: auto;
+  grid-auto-flow: column; grid-auto-columns: minmax(220px, 280px);
+}
+.kanban-column {
+  background: var(--surface); border: 1px solid var(--border); border-radius: 6px;
+  padding: 8px 10px; display: flex; flex-direction: column; gap: 8px;
+  min-height: 120px;
+}
+.kanban-col-head {
+  display: flex; justify-content: space-between; align-items: baseline;
+  border-bottom: 1px solid var(--border); padding-bottom: 6px;
+}
+.kanban-col-label { font-weight: 500; }
+.kanban-cards { list-style: none; padding: 0; margin: 0; display: flex; flex-direction: column; gap: 6px; }
+.kanban-card {
+  background: var(--bg); border: 1px solid var(--border); border-radius: 4px;
+  padding: 6px 8px;
+}
+.kanban-card-title { font-weight: 500; color: var(--fg); text-decoration: none; display: block; }
+.kanban-card-title:hover { color: var(--accent); }
+.kanban-card-meta { display: flex; flex-wrap: wrap; gap: 4px; margin: 4px 0 0; font-size: 0.78em; }
+.kanban-empty { padding: 24px; }
 #tree-filterbar small { opacity: 0.75; margin-left: 2px; }
 .tree-section .empty { padding: 24px; color: var(--muted); }
 .tree-section .clear { color: var(--bad); }
diff --git a/web/templates/tree_kanban.tmpl b/web/templates/tree_kanban.tmpl
new file mode 100644
index 0000000..faebd6a
--- /dev/null
+++ b/web/templates/tree_kanban.tmpl
@@ -0,0 +1,46 @@
+{{/*
+Phase 5i Slice C — kanban view for /tree. Columns by group_by value, cards
+inside each column. Read-only: no drag-to-change (deferred). Empty filtered
+set surfaces a friendly empty-state message.
+*/}}
+{{define "tree-kanban"}}
+<div class="kanban-controls chip-row">
+  <span class="muted">group&nbsp;by:</span>
+  {{range .GroupByChips}}
+    <a class="groupby-chip{{if .Active}} chip-on{{end}}"
+       href="{{.URL}}"
+       hx-get="{{.URL}}" hx-target="#tree-section" hx-swap="outerHTML" hx-push-url="true">{{.Label}}</a>
+  {{end}}
+  <small class="muted">{{.Kanban.Total}} card{{if ne .Kanban.Total 1}}s{{end}}</small>
+</div>
+
+{{if .Kanban.Columns}}
+<div class="kanban-board">
+  {{range .Kanban.Columns}}
+    <section class="kanban-column" data-key="{{.Key}}">
+      <header class="kanban-col-head">
+        <span class="kanban-col-label">{{.Label}}</span>
+        <small class="muted">{{len .Items}}</small>
+      </header>
+      <ul class="kanban-cards">
+        {{range .Items}}
+          <li class="kanban-card">
+            <a class="kanban-card-title" href="/i/{{.PrimaryPath}}">{{.Title}}</a>
+            <p class="kanban-card-meta">
+              <span class="muted">{{.PrimaryPath}}</span>
+              {{range .Management}}<span class="mgmt mgmt-{{.}}">{{.}}</span>{{end}}
+              {{range .Tags}}<span class="tag">{{.}}</span>{{end}}
+              {{if .Pinned}}<span class="pinned" title="Pinned">★</span>{{end}}
+            </p>
+          </li>
+        {{end}}
+      </ul>
+    </section>
+  {{end}}
+</div>
+{{else}}
+<div class="kanban-empty muted">
+  <em>No items match. Try fewer filters or <a href="/?view_type=kanban">clear filters</a>.</em>
+</div>
+{{end}}
+{{end}}
diff --git a/web/templates/tree_section.tmpl b/web/templates/tree_section.tmpl
index f2ef19f..3393d5e 100644
--- a/web/templates/tree_section.tmpl
+++ b/web/templates/tree_section.tmpl
@@ -78,6 +78,8 @@
 
   {{if eq .ViewType "card"}}
     {{template "tree-card" .}}
+  {{else if eq .ViewType "kanban"}}
+    {{template "tree-kanban" .}}
   {{else}}
   <section class="tree">
     <ul class="forest">
diff --git a/web/view_type.go b/web/view_type.go
index 5cbe3e4..ea31c5b 100644
--- a/web/view_type.go
+++ b/web/view_type.go
@@ -66,10 +66,8 @@ func PageViewTypes(route string) ViewTypeSet {
 	case "/", "tree":
 		return ViewTypeSet{
 			Default: ViewTypeList,
-			// Card joins in slice B; kanban lands in slice C — until then,
-			// `?view_type=kanban` falls back to list with the chip strip
-			// labelling it "coming soon" via the template.
-			Allowed: []string{ViewTypeList, ViewTypeCard},
+			// Slice B: list + card. Slice C: kanban joins.
+			Allowed: []string{ViewTypeList, ViewTypeCard, ViewTypeKanban},
 		}
 	case "/dashboard", "dashboard":
 		// Dashboard is locked to its Phase 5h tabbed-tiles surface in slice B.
diff --git a/web/view_type_test.go b/web/view_type_test.go
index e84655b..762520d 100644
--- a/web/view_type_test.go
+++ b/web/view_type_test.go
@@ -16,7 +16,7 @@ func TestParseViewTypeFallsBackOnUnknown(t *testing.T) {
 		{"/", "", ViewTypeList},                     // default for tree
 		{"/", "card", ViewTypeCard},                 // allowed on tree
 		{"/", "list", ViewTypeList},                 // explicit default
-		{"/", "kanban", ViewTypeList},               // not allowed yet → default
+		{"/", "kanban", ViewTypeKanban},             // unlocked in slice C
 		{"/", "junk", ViewTypeList},                 // unknown → default
 		{"/dashboard", "", ViewTypeCard},            // default for dashboard
 		{"/dashboard", "list", ViewTypeCard},        // not allowed in slice B → default
@@ -55,12 +55,16 @@ func TestViewTypeChipsMarkLockedAndActive(t *testing.T) {
 	if byLabel[ViewTypeList].Active {
 		t.Error("list chip should not be Active when current=card")
 	}
-	if byLabel[ViewTypeList].Locked {
-		t.Error("list is allowed on /; chip should not be Locked")
+	for _, allowed := range []string{ViewTypeList, ViewTypeCard, ViewTypeKanban} {
+		if byLabel[allowed].Locked {
+			t.Errorf("%s is allowed on /; chip should not be Locked", allowed)
+		}
 	}
-	for _, locked := range []string{ViewTypeCalendar, ViewTypeKanban, ViewTypeTimeline} {
+	// Slice C only unlocks kanban; calendar + timeline stay locked on /tree
+	// until cross-route view_type swaps land in a future slice.
+	for _, locked := range []string{ViewTypeCalendar, ViewTypeTimeline} {
 		if !byLabel[locked].Locked {
-			t.Errorf("%s should be Locked on / in slice B (not yet implemented)", locked)
+			t.Errorf("%s should still be Locked on /", locked)
 		}
 	}
 }