As I mentioned earlier, you can have multiple Content Place Holders in Master Pages. The Content Place Holders will determine what controls get added to the Content Place Holders. The list of Content Place holders users in SharePoint 2007 and their descriptions can be found at http://office.microsoft.com/en-us/sharepointdesigner/HA101651201033.aspx. You can also create your own content place holders. At one of the client locations I was tasked with creating an area to display external objects. They also needed it in a completely different location on the Master Page. So I created my own Content Holder and the site definition then declared it and added zones to it. The site definition linking with Master Pages is explained later. One of the issues which I faced while creating my master page was which Place Holders I needed to use. I used some of the Content Holders as mentioned in the above application. Most of the pages worked, but as soon as I tried to add a new item or edit an item to the list it started blowing up. Then I realized that most of the content holders mentioned in the document above are required. So, the rule of thumb is to include all of the content holders on the master page. The placement of the content holders can be changed based on the HTML Design and requirements.