diff --git a/README.md b/README.md
index aeda086..69af939 100644
--- a/README.md
+++ b/README.md
@@ -79,6 +79,7 @@ kubectl-tmux_exec --help
 
 Flag | Usage
 --- | ---
+`-V`<br>`--version` | Print the version information
 `-l`<br>`--selector` | Selector (label query) to filter on, supports '=', '==', and '!='.(e.g. -l key1=value1,key2=value2)<br>You must either use `--selector` or `--file` option.
 `-f`<br>`--file` | Read pod names line-by-line from a file.<br>You must either use `--selector` or `--file` option.
 `-c`<br>`--container` | Container name. If omitted, the first container in the pod will be chosen
@@ -87,7 +88,7 @@ Flag | Usage
 `-d`<br>`--detach` | Make the Tmux session detached
 `--remain-on-exit` | Remain Tmux window on exit
 `--select-layout` | One of the five Tmux preset layouts: even-horizontal, even-vertical, main-horizontal, main-vertical, or tiled.
-`-V`<br>`--version` | Print the version information
+`--session-mode` | Where tmux is opened: auto, new-session, current-session
 
 The usage of these options is also available by `--help`.
 
diff --git a/bin/kubectl-tmux_exec b/bin/kubectl-tmux_exec
index 4abdde8..e5ec988 100755
--- a/bin/kubectl-tmux_exec
+++ b/bin/kubectl-tmux_exec
@@ -24,9 +24,9 @@ set -euf -o pipefail
 # Stack Overflow: https://stackoverflow.com/a/246128/1122665
 SOURCE="${BASH_SOURCE[0]}"
 while [[ -h "$SOURCE" ]]; do
-  PROG_DIR="$( cd -P "$( dirname "$SOURCE" )" >/dev/null 2>&1 && pwd )"
-  SOURCE="$(readlink "$SOURCE")"
-  [[ $SOURCE != /* ]] && SOURCE="$PROG_DIR/$SOURCE"
+    PROG_DIR="$( cd -P "$( dirname "$SOURCE" )" >/dev/null 2>&1 && pwd )"
+    SOURCE="$(readlink "$SOURCE")"
+    [[ $SOURCE != /* ]] && SOURCE="$PROG_DIR/$SOURCE"
 done
 PROG_DIR="$( cd -P "$( dirname "$SOURCE" )" >/dev/null 2>&1 && pwd )"
 
@@ -63,6 +63,12 @@ declare -ra TMUX_LAYOUTS=(
     'tiled'
 )
 
+declare -ra SESSION_MODES=(
+    'auto'
+    'new-session'
+    'current-session'
+)
+
 function usage() {
     cat << EOF
 Execute a command in all containers that match the label selector using Tmux.
@@ -87,6 +93,10 @@ Options:
   -l, --selector: Selector (label query) to filter on, supports '=', '==', and '!='.(e.g. -l key1=value1,key2=value2)
   -f, --file: Read pod names line-by-line from a file
   -d, --detach=false: Make the Tmux session detached
+  --session-mode=auto: Where tmux is opened:
+                       new-session (always in a new session no matter whether there is an existing or not)
+                       current-session (re-use the current session)
+                       auto ('current-session' if there is an existing one, otherwise 'new-session')
   --remain-on-exit=false: Remain Tmux window on exit
   --select-layout=tiled: One of the five Tmux preset layouts: even-horizontal, even-vertical, main-horizontal,
                          main-vertical, or tiled.
@@ -157,7 +167,7 @@ function array_contains() {
 function main() {
     local opts
     opts=$(ggetopt -o hVitdc:l:f:"$(printf '%s:' "${KUBECTL_SHORT_OPTS[@]}")" --long \
-        help,version,stdin,tty,detach,container:,selector:,remain-on-exit,select-layout:,file:,"$(printf '%s:,' "${KUBECTL_LONG_OPTS[@]}")","$(printf '%s,' "${KUBECTL_NOARG_LONG_OPTS[@]}")" -- "$@")
+        help,version,stdin,tty,detach,container:,selector:,remain-on-exit,select-layout:,session-mode:,file:,"$(printf '%s:,' "${KUBECTL_LONG_OPTS[@]}")","$(printf '%s,' "${KUBECTL_NOARG_LONG_OPTS[@]}")" -- "$@")
     eval set -- $opts
 
     local selector
@@ -167,6 +177,7 @@ function main() {
     local tmux_layout='tiled'
     local pod_list_file
     local tmux_detach=0
+    local session_mode='auto'
     while [[ $# -gt 0 ]]; do
         local opt="$1"
         case "${opt}" in
@@ -202,6 +213,10 @@ function main() {
                 shift
                 tmux_layout="$1"
                 ;;
+            --session-mode)
+                shift
+                session_mode="$1"
+                ;;
             -f|--file)
                 shift
                 pod_list_file="$1"
@@ -250,7 +265,11 @@ function main() {
     if [[ -z "${tmux_layout}" ]] || ! array_contains "${tmux_layout}" "${TMUX_LAYOUTS[@]}"; then
         error_and_exit "Unknown layout: ${tmux_layout}"
     fi
-    
+
+    if [[ -z "${session_mode}" ]] || ! array_contains "${session_mode}" "${SESSION_MODES[@]}"; then
+        error_and_exit "Unknown session mode: ${session_mode}"
+    fi
+
     local commands=("$@")
 
     local kubectl_exec_opts='-i -t'
@@ -294,10 +313,21 @@ function main() {
     for pod in "${pods[@]}"; do
         local cmd="kubectl ${kubectl_opts[@]:-} exec ${kubectl_exec_opts} ${pod} -- ${exec_cmd_str}"
         if [[ "${#tmux_commands[@]}" -eq 0 ]]; then
+            local open_command
+            if [[ "${session_mode}" == 'new-session' ]]; then
+                open_command='new-session'
+            elif [[ "${session_mode}" == 'current-session' ]]; then
+                open_command='new-window'
+            elif [[ -z "${TMUX:-}" ]]; then
+                open_command='new-session'
+            else
+                open_command='new-window'
+            fi
+
             if [[ "${tmux_detach}" -eq 0 ]]; then
-                tmux_commands+=('new-session' "${cmd}" ';')
+                tmux_commands+=("${open_command}" "${cmd}" ';')
             else
-                tmux_commands+=('new-session' '-d' "${cmd}" ';')
+                tmux_commands+=("${open_command}" '-d' "${cmd}" ';')
             fi
         else
             tmux_commands+=('split-window' "${cmd}" ';')
diff --git a/test/exec-one-pod.bats b/test/exec-one-pod.bats
index 2aedd10..7275422 100644
--- a/test/exec-one-pod.bats
+++ b/test/exec-one-pod.bats
@@ -2,41 +2,12 @@
 
 load test-helper
 
-readonly POD_NAME='alpine'
-readonly POD_APP_LABEL='alpine'
-
 function setup() {
-    kubectl apply -f - << EOF
-apiVersion: v1
-kind: Pod
-metadata:
-  name: ${POD_NAME}
-  labels:
-    app: ${POD_APP_LABEL}
-spec:
-  containers:
-  - name: alpine
-    image: alpine
-    command:
-    - sleep
-    - infinite
-EOF
-    local pod_status=''
-    local retries=30
-    while [[ "${pod_status}" != 'Running' ]]; do
-        sleep 1
-        pod_status="$(kubectl get pods "${POD_NAME}" -o custom-columns=':status.phase' --no-headers)"
-        echo "The pod status is ${pod_status}."
-        (( --retries )) || {
-            echo 'Timed out.'
-            exit 1
-        }
-    done
+    setup_one_pod
 }
 
 function teardown() {
-    kubectl delete pod "${POD_NAME}"
-    sleep 1
+    teardown_one_pod
 }
 
 @test "Exec one pod by label" {
diff --git a/test/nested-tmux.bats b/test/nested-tmux.bats
new file mode 100644
index 0000000..4140b5a
--- /dev/null
+++ b/test/nested-tmux.bats
@@ -0,0 +1,25 @@
+#!/usr/bin/env bats
+
+load test-helper
+
+function setup() {
+    setup_one_pod
+}
+
+function teardown() {
+    teardown_one_pod
+    tmux kill-server || true
+}
+
+@test "Reuse tmux session" {
+    tmux new-session -d bin/kubectl-tmux_exec -l app="${POD_APP_LABEL}" sh
+    [ "$(tmux ls | wc -l)" -eq 1 ]
+}
+
+@test "Nest tmux session" {
+    tmux new-session -d bin/kubectl-tmux_exec -l app="${POD_APP_LABEL}" --session-mode new-session sh
+    sleep 2
+    local tmux_exit_code=0
+    tmux ls || tmux_exit_code="$?"
+    [ "${tmux_exit_code}" -eq 1 ]
+}
diff --git a/test/test-helper.bash b/test/test-helper.bash
index d55bcad..fe92963 100644
--- a/test/test-helper.bash
+++ b/test/test-helper.bash
@@ -9,4 +9,41 @@ function wait_until_no_sessions() {
         }
         sleep 1
     done
+}
+
+readonly POD_NAME='alpine'
+readonly POD_APP_LABEL='alpine'
+
+function setup_one_pod() {
+    kubectl apply -f - << EOF
+apiVersion: v1
+kind: Pod
+metadata:
+  name: ${POD_NAME}
+  labels:
+    app: ${POD_APP_LABEL}
+spec:
+  containers:
+  - name: alpine
+    image: alpine
+    command:
+    - sleep
+    - infinite
+EOF
+    local pod_status=''
+    local retries=30
+    while [[ "${pod_status}" != 'Running' ]]; do
+        sleep 1
+        pod_status="$(kubectl get pods "${POD_NAME}" -o custom-columns=':status.phase' --no-headers)"
+        echo "The pod status is ${pod_status}."
+        (( --retries )) || {
+            echo 'Timed out.'
+            exit 1
+        }
+    done
+}
+
+function teardown_one_pod() {
+    kubectl delete pod "${POD_NAME}"
+    sleep 5
 }
\ No newline at end of file