The biggest difference between memoirs and autobiographies is the time period that is covered in each genre. Both are nonfiction, factual accounts based on the author's life, written in the first person. A memoir tells a specific story from a particular period of the author's life, whereas an autobiography tells the entire story of the author's life. A memoir may focus on a particular time period, a stage of life that is important, or a series of connected events. An autobiography typically includes all aspects of the author's life up to the point when it is written, though certain events may receive more or less emphasis in order to emphasize a particular theme or overarching message.  Consider whether you want to write about your entire life, from the beginning to the present, or whether you want to concentrate on a specific time period when deciding whether to write a memoir or an autobiography.