This book constitutes the thoroughly refereed post-conference proceedings of the 4th International Symposium on Trustworthy Global Computing, TGC 2008 held in Barcelona, Spain, in November 2008. The 12 revised papers presented together with one invited paper were carefully selected from 26 submissions during two rounds of reviewing and improvement. The TGC 2008 symposium papers focus on providing tools and frameworks for constructing well-behaved applications and for reasoning about their behavior and properties in models of computation that incorporate code and data mobility over distributed networks with highly dynamic topologies and heterogeneous devices.