Sample Code
1 protected void Button1_Click(object sender, EventArgs e)
2 {
3 this.TextBox1.Text = this.Button1.ID;
4 this.TextBox2.Text = this.Button1.ClientID;
5 this.TextBox3.Text = this.Button1.UniqueID;
6 }
http://blogs.telerik.com/AtanasKorchev/Posts/08-06-06/The_difference_between_ID_ClientID_and_UniqueID.aspx