  This volume contains the papers presented at the 6th conference on Machines,
Computations and Universality (MCU 2013). MCU 2013 was held in Zurich,
Switzerland, September 9-11, 2013. The MCU series began in Paris in 1995 and
has since been concerned with gaining a deeper understanding of computation
through the study of models of general purpose computation. This volume
continues in this tradition and includes new simple universal models of
computation, and other results that clarify the relationships between models.
