diff --git a/internal/tui/mouse.go b/internal/tui/mouse.go
new file mode 100644
index 0000000..5bbedeb
--- /dev/null
+++ b/internal/tui/mouse.go
@@ -0,0 +1,132 @@
+package tui
+
+import tea "github.com/charmbracelet/bubbletea"
+
+// Layout offsets for hit-testing the rendered views (see view.go). Every
+// screen renders a title line then a blank line before its content, so content
+// starts at headerRows. The grid is drawn with a border between cells, hence
+// the +1s.
+const (
+	headerRows = 2          // title line + blank line
+	cellStride = cellW + 1  // cell inner width + right border column
+	blockH     = cellH + 1  // cell content rows + top border row
+)
+
+// handleMouse routes mouse events per screen. Enables click-to-select on the
+// list screens and tmux-style click/drag editing in the layout grid.
+func (m *model) handleMouse(msg tea.MouseMsg) (tea.Model, tea.Cmd) {
+	switch m.screen {
+	case screenMenu, screenCameras, screenLayouts, screenSetActive:
+		return m.mouseList(msg)
+	case screenLayoutEdit:
+		return m.mouseGridEdit(msg)
+	case screenCameraPicker:
+		return m.mousePicker(msg)
+	}
+	return m, nil
+}
+
+// cellAtMouse maps a screen position to a grid cell in the editor/picker.
+func (m *model) cellAtMouse(x, y int) (col, row int, ok bool) {
+	cols, rows := m.gridDims()
+	if y < headerRows || x < 0 {
+		return 0, 0, false
+	}
+	row = (y - headerRows) / blockH
+	col = x / cellStride
+	if row < 0 || row >= rows || col < 0 || col >= cols {
+		return 0, 0, false
+	}
+	return col, row, true
+}
+
+// gridLineCount is how many terminal rows renderGrid emits.
+func (m *model) gridLineCount() int {
+	_, rows := m.gridDims()
+	return rows*blockH + 1
+}
+
+// listLen is the number of selectable rows on the current list screen.
+func (m *model) listLen() int {
+	switch m.screen {
+	case screenMenu:
+		return len(menuItems)
+	case screenCameras:
+		return len(m.cfg.Cameras)
+	case screenLayouts, screenSetActive:
+		return len(m.cfg.Layouts)
+	}
+	return 0
+}
+
+// mouseList: left-click a row to select and activate it (same as pressing enter).
+func (m *model) mouseList(msg tea.MouseMsg) (tea.Model, tea.Cmd) {
+	if msg.Action != tea.MouseActionRelease || msg.Button != tea.MouseButtonLeft {
+		return m, nil
+	}
+	idx := msg.Y - headerRows
+	if idx < 0 || idx >= m.listLen() {
+		return m, nil
+	}
+	m.cursor = idx
+	return m.handleKey(tea.KeyMsg{Type: tea.KeyEnter})
+}
+
+// mouseGridEdit implements tmux-style editing: click a cell to assign a camera,
+// or press on a tile and drag to resize its span (grid-snapped).
+func (m *model) mouseGridEdit(msg tea.MouseMsg) (tea.Model, tea.Cmd) {
+	if msg.Button != tea.MouseButtonLeft {
+		return m, nil
+	}
+	col, row, ok := m.cellAtMouse(msg.X, msg.Y)
+	switch msg.Action {
+	case tea.MouseActionPress:
+		if !ok {
+			return m, nil
+		}
+		m.edCol, m.edRow = col, row
+		m.dragTile = m.tileIndexAt(col, row)
+		m.dragging = m.dragTile >= 0
+		m.dragMoved = false
+
+	case tea.MouseActionMotion:
+		if !ok || !m.dragging {
+			return m, nil
+		}
+		t := &m.curLayout().Tiles[m.dragTile]
+		newCS, newRS := col-t.Col+1, row-t.Row+1
+		// Only grow/shrink toward the bottom-right of the tile's origin.
+		if newCS >= 1 && newRS >= 1 && m.regionFree(m.dragTile, t.Col, t.Row, newCS, newRS) {
+			t.ColSpan, t.RowSpan = newCS, newRS
+			m.edCol, m.edRow = col, row
+			m.dragMoved = true
+			m.dirty = true
+		}
+
+	case tea.MouseActionRelease:
+		wasDrag := m.dragging && m.dragMoved
+		m.dragging = false
+		m.dragMoved = false
+		// A plain click (no drag) opens the camera picker for that cell.
+		if ok && !wasDrag {
+			m.edCol, m.edRow = col, row
+			m.screen, m.cursor = screenCameraPicker, 0
+		}
+	}
+	return m, nil
+}
+
+// mousePicker: left-click an option to choose it.
+func (m *model) mousePicker(msg tea.MouseMsg) (tea.Model, tea.Cmd) {
+	if msg.Action != tea.MouseActionRelease || msg.Button != tea.MouseButtonLeft {
+		return m, nil
+	}
+	// Options are drawn below the grid and a blank separator line.
+	optStart := headerRows + m.gridLineCount() + 1
+	idx := msg.Y - optStart
+	if idx < 0 || idx >= len(m.pickerOptions()) {
+		return m, nil
+	}
+	m.cursor = idx
+	return m.handleKey(tea.KeyMsg{Type: tea.KeyEnter})
+}
diff --git a/internal/tui/mouse_test.go b/internal/tui/mouse_test.go
new file mode 100644
index 0000000..ac76847
--- /dev/null
+++ b/internal/tui/mouse_test.go
@@ -0,0 +1,33 @@
+package tui
+
+import (
+	"testing"
+
+	"github.com/lwoodard/rtsp-streamer/internal/config"
+)
+
+func TestCellAtMouse(t *testing.T) {
+	m := &model{
+		cfg:        &config.Config{Layouts: []config.Layout{{Name: "g", Grid: "3x3"}}},
+		editLayout: 0,
+	}
+	cases := []struct {
+		x, y          int
+		wantCol, wRow int
+		ok            bool
+	}{
+		{1, 3, 0, 0, true},   // first content row, first cell
+		{12, 3, 1, 0, true},  // second column (x past the divider at 11)
+		{1, 6, 0, 1, true},   // second grid row
+		{23, 9, 2, 2, true},  // third column, third row
+		{1, 1, 0, 0, false},  // in the title/blank header area
+		{1, 12, 0, 0, false}, // below the 3x3 grid
+	}
+	for _, tc := range cases {
+		col, row, ok := m.cellAtMouse(tc.x, tc.y)
+		if ok != tc.ok || (ok && (col != tc.wantCol || row != tc.wRow)) {
+			t.Errorf("cellAtMouse(%d,%d) = (%d,%d,%v), want (%d,%d,%v)",
+				tc.x, tc.y, col, row, ok, tc.wantCol, tc.wRow, tc.ok)
+		}
+	}
+}
diff --git a/internal/tui/tui.go b/internal/tui/tui.go
index 77a6f7b..9ef8d9c 100644
--- a/internal/tui/tui.go
+++ b/internal/tui/tui.go
@@ -60,6 +60,11 @@ type model struct {
 	editLayout   int // index into cfg.Layouts for edit/picker screens
 	edCol, edRow int // grid-editor cursor position
 
+	// Mouse drag state for tmux-style tile resizing in the grid editor.
+	dragging  bool
+	dragTile  int
+	dragMoved bool
+
 	status  string
 	isError bool
 }
@@ -71,7 +76,7 @@ func Run(cfgPath string) error {
 		return err
 	}
 	m := &model{cfgPath: cfgPath, cfg: cfg, screen: screenMenu}
-	_, err = tea.NewProgram(m, tea.WithAltScreen()).Run()
+	_, err = tea.NewProgram(m, tea.WithAltScreen(), tea.WithMouseCellMotion()).Run()
 	return err
 }
 
@@ -141,6 +146,8 @@ func (m *model) Update(msg tea.Msg) (tea.Model, tea.Cmd) {
 			m.setStatus("saved to "+m.cfgPath, false)
 		}
 		return m, nil
+	case tea.MouseMsg:
+		return m.handleMouse(msg)
 	case tea.KeyMsg:
 		return m.handleKey(msg)
 	}
diff --git a/internal/tui/view.go b/internal/tui/view.go
index 9efe1a1..cea52b5 100644
--- a/internal/tui/view.go
+++ b/internal/tui/view.go
@@ -106,6 +106,7 @@ func (m *model) viewLayoutEdit() string {
 	b.WriteString(m.renderGrid(cols, rows))
 	b.WriteString("\n\n")
 	b.WriteString(strings.Join([]string{
+		hkey("click", "assign cell") + "    " + hkey("drag a tile", "resize") + "  (mouse)",
 		hkey("←↑↓→/hjkl", "move") + "    " + hkey("enter", "assign") + "    " + hkey("c", "clear"),
 		"resize tile  " + hkey("L/H", "wider/narrower") + "    " + hkey("J/K", "taller/shorter"),
 		"base grid  " + hkey("] [", "cols") + "    " + hkey("} {", "rows") + "    " + hkey("esc", "back"),