How to make linked drop down box

Hi, there, Could someone tell how to implement a two or more drop down list with parent and child relationship between them? What I need is something like the following. For example, if click on country, we will see "US< Canada, France, etc". After click on "US", we can see "Arizona, California, Florida, etc" in State box. After click on California in State box, we can see " san Jose, San Francisco, Santa Clara, etc" in City box. Thank you in advance! Henry Position Type : -- Select -- Country : -- Select --U.S.BelgiumChinaIndiaIsraelJapanNetherlandsSingaporeTaiwanUnited KingdomKorea State : -- Select -- City : -- Select --