Effective planning for community health partnerships requires understanding how initial readiness—that is, contextual factors and capacity—influences implementation of activities and programs. This study compares the context and capacity of drug and violence prevention coalitions in Mexico to those in the United States. Measures of coalition context include community problems, community leadership style, and sense of community. Measures of coalition capacity include the existence of collaborative partnerships and coalition champions. The assessment was completed by 195 members of 9 coalitions in Mexico and 139 members of 7 coalitions in the United States. Psychometric analyses indicate the measures have moderate to strong internal consistency, along with good convergent and discriminant validity in both settings. Results indicate that members of Mexican coalitions perceive substantially more serious community problems, especially with respect to education, law enforcement, and access to alcohol and drugs. Compared to respondents in the United States, Mexican respondents perceive sense of community to be weaker and that prevention efforts are not as valued by the population where the coalitions are located. The Mexican coalitions appear to be operating in a substantially more challenging environment for the prevention of violence and substance use. Their ability to manage these challenges will likely play a large role in determining whether they are successful in their prevention efforts. The context and capacity assessment is a valuable tool that coalitions can use in order to identify and address initial barriers to success.