L. Sprague de Camp was a master of the time travel and alternate history story. In many respects his novel Lest Darkness Fall founded alternate history, while "Aristotle and the Gun" is probably one of the best stories about tinkering with history ever written. In addition we include stories of time travel both backwards and forwards and de Camp's wonderful essay "Language for Time-Travelers". This is a collection of L. Sprague de Camp's SF best stories and essays dealing with time travel. It is the first volume of a projected series of stories and novels by L. Sprague de Camp.