This thesis presents advances in the fabrication and application of multicore optical fibres, specifically pertaining to nonlinear endomicroscopy. Chapters 1 and 2 present the necessary background material to understanding the results presented in chapters 3 and 4. Through chapter 1 the properties of optical fibres are described. The basic structure of silica fibres and the parameters used to classify them are discussed. Typical methods of fabrication are outlined along with post fabrication processes. The experimental procedures required in the later stages of the thesis are also covered. Chapter 2 introduces and reviews nonlinear endoscopy. Various nonlinear process involved are described and the current positions of each in the field of nonlinear imaging discussed. In chapter 3 a method for minimising the variation in group indices of cores within a multicore fibre is outlined, experimentally examined and verified. The minimisation is achieved by specifically controlling the core diameters within the multicore fibre for a given wavelength. The fourth chapter introduces a ‘proof of concept’ method for reducing the bend sensitivity of a multicore fibre. Here a helical path is followed by the cores within the fibre. The specific challenges of fabrication are also described.