This book constitutes the thoroughly refereed post-proceedings of the 11th International Workshop on DNA Based Computers, DNA11, held in London, ON, Canada, in June 2005. The 34 revised full papers presented were carefully selected during two rounds of reviewing and improvement from an initial total of 79 submissions. The wide-ranging topics include in vitro and in vivo biomolecular computation, algorithmic self-assembly, DNA device design, DNA coding theory, and membrane computing.