The biological functions of DNA rest on the ability of complementary nucleic acid strands to adopt the iconic Watson-Crick double helix. The driving force for the assembly of this structure is the formation of specific A-T and G-C base-pairs. The order of bases along a particular strand encodes crucial biological information, which is decoded by specialized enzymes within a cell that can 'read' the order of the base-pairs directly. However, DNA itself is a powerful computational device; due specifically to the ability of one DNA strand to locate, and pair with, only its exact complementary strand - even when present with millions of non-complementary, competing sequences. This property has lead to DNA being exploited to solve efficiently a case of the travelling salesman problem. This ability of DNA also makes computationally 'hard' problems amenable to DNA-based solution methods, and could offer a novel approach to resolving the P = NP question.