A novel technique for maximum “a posteriori” (MAP) adaptation of maximum entropy (MaxEnt) and maximum entropy Markov models (MEMM) is presented. The technique is applied to the problem of recovering the correct capitalization of uniformly cased text: a “background” capitalizer trained on 20Mwds of Wall Street Journal (WSJ) text from 1987 is adapted to two Broadcast News (BN) test sets — one containing ABC Primetime Live text and the other NPR Morning News/CNN Morning Edition text — from 1996. The “in-domain” performance of the WSJ capitalizer is 45% better than that of the 1-gram baseline, when evaluated on a test set drawn from WSJ 1994. When evaluating on the mismatched “out-ofdomain” test data, the 1-gram baseline is outperformed by 60%; the improvement brought by the adaptation technique using a very small amount of matched BN data — 25-70kwds — is about 20-25% relative. Overall, automatic capitalization error rate of 1.4% is achieved on BN data.