This is prompted by Margaret S's good summary of organizing your genealogical files. A cousin of my wife had developed a coding system which I used prior to my present computer program, which seems to me simple, useful, and elegant: It is based on an ancestry chart. Using binary coding of 1 for male and 0 for female. My code would be 1, my wife's 0, my paternal grandfather would be 111, her grandmother on her father's side would be 010, and so on. I think it could be a basis for a file drawer filing system. As the numbers get longer, just group them by threes: 100-111 would be my maternal grandmother's great grandfather in her father's line.