I hope I have this right! A biography is a book written about a person, living or dead, who is not the author. An autobiography, or memoir, is a book written about oneself.

additionally...autobiographies are focused on the entire life of the author. A memoir features anecdotes about people they've known and places they've been.

One is needed to create the other ... Memoirs are what is needed to establish the biography ... (the biography is the finished result of ones memoirs accumulated to write and describe a past life time) Its knowledge of past life time that is needed to create the biography ... Without memoirs ... you have no true knowledge of ones past to create it. Memoirs accumulated and written = Biography :)

Let's see ... if you are the writer, then ... Autobiography - a book about yourself that includes your entire lifeline .. birth to current day. Biography - similar to the above except that it's about someone else and THEIR entire lifeline .. birth to current or to death if done after they've died. Memoir - a book about yourself that while it's about your own life, it's typically NOT about your entire life. Instead, it tends to have a THEME or "slice of life" or period of time .. ie something that narrows the focus of what you CHOOSE from your life to include. In a sense, it's tougher to pull off than biography as it's a form of "creative non-fiction" .. ie .. it has to be factual .. based on truth .. but also has to be in a form (your theme or ARC of "story") .. that is entertaining or engaging. The thread or segment of your life .. that purposely chosen .. might show a challenge overcome or some other theme. The reader should be able to identify and want to know more of "that life" - "that world" - You - what you experienced - decided - felt - thought - and ultimately - what you learned from it. The arc. Autobiography and biography were easier to define. A memoir, on the other hand, is in my mind, a little harder to describe - and write. But really "good" if a writer can pull it off. :)

Memoirs are memories written by the author who is remembering them. That person has to be alive when they are written. They are not about the whole life of the author, either. A biography is about the life of the author. If written by that person, it is an autobiography. A biography can be by anybody who studied the life of that person.

Biography is written by someone about someone's whole life. A memoir is a first hand experience of a part of the writer's life.