Unlike Mainland China, Hong Kong is visa free for US citizens that are visiting for 90 days or less. So all we Americans need to worry about is making sure our US passports have not expired. If you are not a US citizen and want to check if you will need a visa or not, go to this page served up by the Hong Kong Immigration Department. The table is in part 2, number 12 on the page.
Bill is a Midwestern American whose wife is from Hong Kong. He has three daughters and the entire family visits Hong Kong almost every year.