Novel results on the optical binding of optically-trapped micro-particles are presented. A sophisticated Mie scattering model is developed, capable of performing time-evolution simulations of a multi-particle system. This is used to analyse and interpret experimental results in evanescent and Gaussian beam traps, and to develop simple, intuitive explanations for the observed phenomena. Novel trapped states are reported, that do not conform to the symmetry of the underlying trap. A common theme throughout this thesis is the "emergent'' phenomena that occur when multiple particles are trapped together, which cannot easily be predicted by considering each particle in isolation.