This volume contains the papers presented at the 13th International Wo- shop on Approximation Algorithms for Combinatorial Optimization Problems (APPROX 2010) and the 14th International Workshop on Randomization and Computation (RANDOM 2010), which took place concurrently in Universitat Politècnica de Catalunya (UPC) Barcelona, Spain, during September 1-3, 2010. APPROX focuses on algorithmic and complexity issues surrounding the dev- opment of e'cient approximate solutions to computationally di'cult problems, and was the 13th in the series after Aalborg (1998), Berkeley (1999), Sa- brücken (2000), Berkeley (2001), Rome (2002), Princeton (2003), Cambridge (2004), Berkeley (2005), Barcelona (2006), Princeton (2007), Boston (2008) and Berkeley (2009). RANDOM is concerned with applications of randomness to computational and combinatorial problems, and was the 14th workshop in the - ries following Bologna (1997), Barcelona (1998), Berkeley (1999), Geneva (2000), Berkeley (2001), Harvard (2002), Princeton (2003), Cambridge (2004), Berkeley (2005), Barcelona (2006), Princeton (2007), Boston (2008), and Berkeley (2009).