This commentary surveys some of the trends and gaps in current research on criminal justice reform in Latin America – with a focus on Brazil, and on two specific areas: police and prison/penal reform. It explores two principal themes: the uneven and thin production of knowledge about criminal justice issues; and the impact this has on policy reforms and on the ways in which these are framed and interpreted in terms of their relative success and failure. Overall it argues that we still know very little about criminal justice institutions and the actors within them. We also need many more finely-grained analyses of the dynamics of reform efforts and of the policy environments in which these take place in order to understand how and why reform initiatives are often derailed or subverted, and, more rarely, flourish and can be embedded and replicated.