diff --git a/listbox.go b/listbox.go
index 20f1ffd..681c972 100644
--- a/listbox.go
+++ b/listbox.go
@@ -26,7 +26,32 @@ func NewListbox(multiple bool, items ...string) (l *Listbox) {
 	return l
 }
 
-// TODO Append, InsertBefore, Delete
+// Append adds an item to the end of the Listbox's list.
+func (l *Listbox) Append(what string) (err error) {
+	l.lock.Lock()
+	defer l.lock.Unlock()
+
+	if l.created {
+		return l.sysData.append(what)
+	}
+	l.initItems = append(l.initItems, what)
+	return nil
+}
+
+// InsertBefore inserts a new item in the Listbox before the item at the given position.
+func (l *Listbox) InsertBefore(what string, before int) (err error) {
+	l.lock.Lock()
+	defer l.lock.Unlock()
+
+	if l.created {
+		return l.sysData.insertBefore(what, before)
+	}
+	m := make([]string, 0, len(l.initItems) + 1)
+	m = append(m, l.initItems[:before]...)
+	m = append(m, what)
+	l.initItems = append(m, l.initItems[before:]...)
+	return nil
+}
 
 // TODO Selection
 
diff --git a/main.go b/main.go
index 3e87fd1..ce773ed 100644
--- a/main.go
+++ b/main.go
@@ -12,18 +12,20 @@ func main() {
 	c := NewCheckbox("Check Me")
 	cb1 := NewCombobox(true, "You can edit me!", "Yes you can!", "Yes you will!")
 	cb2 := NewCombobox(false, "You can't edit me!", "No you can't!", "No you won't!")
-	i := 0
-	doAdjustments := func() {
-		cb1.Append("append")
-		cb2.InsertBefore(fmt.Sprintf("before %d", i), 1)
-		i++
-	}
-	doAdjustments()
 	e := NewLineEdit("Enter text here too")
 	l := NewLabel("This is a label")
 	s0 := NewStack(Vertical, b, c, cb1, cb2, e, l)
 	lb := NewListbox(true, "Select One", "Or More", "To Continue")
 	lb2 := NewListbox(false, "Select", "Only", "One", "Please")
+	i := 0
+	doAdjustments := func() {
+		cb1.Append("append")
+		cb2.InsertBefore(fmt.Sprintf("before %d", i), 1)
+		lb.InsertBefore(fmt.Sprintf("%d", i), 2)
+		lb2.Append("Please")
+		i++
+	}
+	doAdjustments()
 	s1 := NewStack(Vertical, lb2, lb)
 	s := NewStack(Horizontal, s1, s0)
 	err := w.Open(s)