Previous studies show that close friends improve at lie detection over time. However, is this improvement due to an increase in the ability to decode the feelings of close friends or a change in how close friends communicate their true and deceptive emotions? In a study of 45 pairs of friends, one friend from each pair (the "sender") was videotaped showing truthful and faked affect in response to pleasant and unpleasant movie clips. The other friend from each pair (the "judge") guessed the true emotions of both the friend and a stranger 1 month and 6 months into the friendship. Judges were better at guessing the true emotions of friends than strangers, and this advantage in judging friends increased among close friends over time. Surprisingly, improvement over time was due mostly to a change in the sender’s communication, rather than an increase in judges’ ability to decode their friends’ feelings.