diff --git a/CHANGELOG.md b/CHANGELOG.md
index 67b5a1df..0299d3b8 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -21,6 +21,7 @@
   the Wayland window.
 * **title** option to `footrc`, that sets the initial window title.
 * `--title` command line option, that sets the initial window title.
+* Right mouse button extends the current selection.
 
 ### Changed
 
diff --git a/README.md b/README.md
index 8f5cc079..18dfc559 100644
--- a/README.md
+++ b/README.md
@@ -163,6 +163,9 @@ These are the default shortcuts. See `man 5 foot` and the example
 <kbd>middle</kbd>
 : Paste from _primary_ selection
 
+<kbd>right</kbd>
+: Extend current selection
+
 <kbd>wheel</kbd>
 : Scroll up/down in history
 
diff --git a/doc/foot.1.scd b/doc/foot.1.scd
index 7c2dbccd..551b6a33 100644
--- a/doc/foot.1.scd
+++ b/doc/foot.1.scd
@@ -194,6 +194,9 @@ Note that these are just the defaults; they can be changed in the
 *middle*
 	Paste from the _primary_ selection
 
+*right*
+	Extend current selection
+
 *wheel*
 	Scroll up/down in history
 
diff --git a/input.c b/input.c
index 4fff710f..22cefa1e 100644
--- a/input.c
+++ b/input.c
@@ -1174,7 +1174,9 @@ wl_pointer_button(void *data, struct wl_pointer *wl_pointer,
 
         switch (state) {
         case WL_POINTER_BUTTON_STATE_PRESSED: {
-            if (button == BTN_LEFT) {
+            if (button == BTN_LEFT && wayl->mouse.count <= 3) {
+                selection_cancel(term);
+
                 switch (wayl->mouse.count) {
                 case 1:
                     selection_start(
@@ -1193,6 +1195,10 @@ wl_pointer_button(void *data, struct wl_pointer *wl_pointer,
                 }
             }
 
+            else if (button == BTN_RIGHT && wayl->mouse.count == 1) {
+                selection_extend(term, wayl->mouse.col, wayl->mouse.row, serial);
+            }
+
             else {
                 for (size_t i = 0; i < ALEN(wayl->conf->bindings.mouse); i++) {
                     const struct mouse_binding *binding =
@@ -1211,7 +1217,6 @@ wl_pointer_button(void *data, struct wl_pointer *wl_pointer,
                     execute_binding(term, binding->action, serial);
                     break;
                 }
-                selection_cancel(term);
             }
 
             term_mouse_down(term, button, wayl->mouse.row, wayl->mouse.col);
@@ -1219,9 +1224,7 @@ wl_pointer_button(void *data, struct wl_pointer *wl_pointer,
         }
 
         case WL_POINTER_BUTTON_STATE_RELEASED:
-            if (button != BTN_LEFT || term->selection.end.col == -1)
-                selection_cancel(term);
-            else
+            if (button == BTN_LEFT && term->selection.end.col != -1)
                 selection_finalize(term, serial);
 
             term_mouse_up(term, button, wayl->mouse.row, wayl->mouse.col);
diff --git a/selection.c b/selection.c
index 189119d9..534a0888 100644
--- a/selection.c
+++ b/selection.c
@@ -335,6 +335,32 @@ mark_selected(struct terminal *term, struct row *row, struct cell *cell,
     cell->attrs.clean = 0;
 }
 
+static void
+selection_modify(struct terminal *term, struct coord start, struct coord end)
+{
+    assert(selection_enabled(term));
+    assert(term->selection.start.row != -1);
+    assert(start.row != -1 && start.col != -1);
+    assert(end.row != -1 && end.col != -1);
+
+    /* Premark all cells that *will* be selected */
+    foreach_selected(term, start, end, &premark_selected, NULL);
+
+    if (term->selection.end.row != -1) {
+        /* Unmark previous selection, ignoring cells that are part of
+         * the new selection */
+        foreach_selected(term, term->selection.start, term->selection.end,
+                         &unmark_selected, NULL);
+    }
+
+    term->selection.start = start;
+    term->selection.end = end;
+
+    /* Mark new selection */
+    foreach_selected(term, start, end, &mark_selected, NULL);
+    render_refresh(term);
+}
+
 void
 selection_update(struct terminal *term, int col, int row)
 {
@@ -350,26 +376,159 @@ selection_update(struct terminal *term, int col, int row)
     assert(term->grid->view + row != -1);
 
     struct coord new_end = {col, term->grid->view + row};
+    selection_modify(term, term->selection.start, new_end);
+}
 
-    /* Premark all cells that *will* be selected */
-    foreach_selected(
-        term, term->selection.start, new_end, &premark_selected, NULL);
+static void
+selection_extend_normal(struct terminal *term, int col, int row, uint32_t serial)
+{
+    const struct coord *start = &term->selection.start;
+    const struct coord *end = &term->selection.end;
 
-    if (term->selection.end.row != -1) {
-        /* Unmark previous selection, ignoring cells that are part of
-         * the new selection */
-        foreach_selected(term, term->selection.start, term->selection.end,
-                         &unmark_selected, NULL);
+    if (start->row > end->row ||
+        (start->row == end->row && start->col > end->col))
+    {
+        const struct coord *tmp = start;
+        start = end;
+        end = tmp;
     }
 
-    term->selection.end = new_end;
-    assert(term->selection.start.row != -1 && term->selection.end.row != -1);
+    assert(start->row < end->row || start->col < end->col);
 
-    /* Mark new selection */
-    foreach_selected(
-        term, term->selection.start, term->selection.end, &mark_selected, NULL);
+    struct coord new_start, new_end;
 
-    render_refresh(term);
+    if (row < start->row || (row == start->row && col < start->col)) {
+        /* Extend selection to start *before* current start */
+        new_start = (struct coord){col, row};
+        new_end = *end;
+    }
+
+    else if (row > end->row || (row == end->row && col > end->col)) {
+        /* Extend selection to end *after* current end */
+        new_start = *start;
+        new_end = (struct coord){col, row};
+    }
+
+    else {
+        /* Shrink selection from start or end, depending on which one is closest */
+
+        const int linear = row * term->cols + col;
+
+        if (abs(linear - (start->row * term->cols + start->col)) <
+            abs(linear - (end->row * term->cols + end->col)))
+        {
+            /* Move start point */
+            new_start = (struct coord){col, row};
+            new_end = *end;
+        }
+
+        else {
+            /* Move end point */
+            new_start = *start;
+            new_end = (struct coord){col, row};
+        }
+    }
+
+    selection_modify(term, new_start, new_end);
+}
+
+static void
+selection_extend_block(struct terminal *term, int col, int row, uint32_t serial)
+{
+    const struct coord *start = &term->selection.start;
+    const struct coord *end = &term->selection.end;
+
+    struct coord top_left = {
+        .row = min(start->row, end->row),
+        .col = min(start->col, end->col),
+    };
+
+    struct coord top_right = {
+        .row = min(start->row, end->row),
+        .col = max(start->col, end->col),
+    };
+
+    struct coord bottom_left = {
+        .row = max(start->row, end->row),
+        .col = min(start->col, end->col),
+    };
+
+    struct coord bottom_right = {
+        .row = max(start->row, end->row),
+        .col = max(start->col, end->col),
+    };
+
+    struct coord new_start;
+    struct coord new_end;
+
+    if (row <= top_left.row ||
+        abs(row - top_left.row) < abs(row - bottom_left.row))
+    {
+        /* Move one of the top corners */
+
+        if (abs(col - top_left.col) < abs(col - top_right.col)) {
+            new_start = (struct coord){col, row};
+            new_end = bottom_right;
+        }
+
+        else {
+            new_start = (struct coord){col, row};
+            new_end = bottom_left;
+        }
+    }
+
+    else {
+        /* Move one of the bottom corners */
+
+        if (abs(col - bottom_left.col) < abs(col - bottom_right.col)) {
+            new_start = top_right;
+            new_end = (struct coord){col, row};
+        }
+
+        else {
+            new_start = top_left;
+            new_end = (struct coord){col, row};
+        }
+    }
+
+    selection_modify(term, new_start, new_end);
+}
+
+void
+selection_extend(struct terminal *term, int col, int row, uint32_t serial)
+{
+    if (!selection_enabled(term))
+        return;
+
+    if (term->selection.start.row == -1 || term->selection.end.row == -1) {
+        /* No existing selection */
+        return;
+    }
+
+    row += term->grid->view;
+
+    if ((row == term->selection.start.row && col == term->selection.start.col) ||
+        (row == term->selection.end.row && col == term->selection.end.col))
+    {
+        /* Extension point *is* one of the current end points */
+        return;
+    }
+
+    switch (term->selection.kind) {
+    case SELECTION_NONE:
+        assert(false);
+        return;
+
+    case SELECTION_NORMAL:
+        selection_extend_normal(term, col, row, serial);
+        break;
+
+    case SELECTION_BLOCK:
+        selection_extend_block(term, col, row, serial);
+        break;
+    }
+
+    selection_to_primary(term, serial);
 }
 
 static const struct zwp_primary_selection_source_v1_listener primary_selection_source_listener;
diff --git a/selection.h b/selection.h
index bc690eb1..5bc216e1 100644
--- a/selection.h
+++ b/selection.h
@@ -14,6 +14,7 @@ void selection_start(
 void selection_update(struct terminal *term, int col, int row);
 void selection_finalize(struct terminal *term, uint32_t serial);
 void selection_cancel(struct terminal *term);
+void selection_extend(struct terminal *term, int col, int row, uint32_t serial);
 
 bool selection_on_row_in_view(const struct terminal *term, int row_no);