This project is primarily a study of the actor model of concurrent computation, structured around the design of Merlin, a simple actor-based programming language intended primarily to explore aspects of actor-based language design. The report gives an introduction to the basic concepts of concurrency, concurrent computation models, and the actor model in particular. An extensive documentation of the design process of Merlin is given, with the main focus on analyzing the different language design options available within the actor-based programming paradigm. Each of the design decisions taken during the Merlin design process is justified and put into perspective, by contrasting them with a selection of other actor languages. Finally, a simple abstract-syntax interpreter for the Merlin language is developed and documented. This work highlights some of the design issues of actor-based programming languages, including concurrency issues, language design and implementation challenges.