We document and study the migration of convertible debt offerings from the public to the 144A market during 1991-2004. Over 88% of the 144A convertible debt issues are subsequently registered. An analysis of financing costs (gross spreads, yields, and stock price announcements) and issue characteristics indicates that convertible debt issues in these two markets are essentially the same. We find evidence that the 144A market allows firms to better time equity market conditions. Our findings are consistent with the hypothesis that the 144A market is attractive because it allows firms to issue convertible debt more quickly.