Multicopy Aloha is a generalization of single-copy Aloha where multiple copies of a packet are transmitted without first learning whether the transmission of the first copy is successful or not. Different users in the system Can transmit different number of copies. But the optimal multicopy policy is found to be of the "pure" type whereby all users transmit the same number of copies. To maximize the probability of successful transmission we found that the optimal copy number is one for the normalized channel traffic LAMBDA in range 0.48 < LAMBDA less-than-or-equal-to 1, two for 0.28 < LAMBDA less-than-or-equal-to 0.48, three for 0.20 < LAMBDA less-than-or-equal-to 0.28, etc. Potential applications of multicopy Aloha include packet satellite systems, multichannel Aloha systems and reservation Aloha systems.