Also known simply as a Dear Colleague, this is a type of letter sent by a member(s) of either the House or Senate to other members of that chamber of Congress. Typically, a Dear Colleague asks for members of Congress to support an issue, cosponsor/support legislation, or sign a letter in support of an issue or bill.  Dear Colleague letters are an internal Congressional advocacy tool to help make Members of Congress aware of issues, garner additional support, and then seek a particular action either by fellow Members of Congress, the White House, or a federal agency.  The letters can be sent electronically or hard copy and advocacy organizations often work with elected officials to have Dear Colleague letters circulated on their issues of concern and priority.