On defects in affine Toda field theory

This thesis outlines methods for generating new integrable defects in affine Toda field theory. These methods are grounded in the hypothesis that defects have a particle-like classification with as many species of fundamental defect existing in a particular affine Toda theory as there are species of soliton. The methods employed are: 1. Defect fusing rules, linking different species of defect in the same theory. Defect fusing rules are used in this thesis to find transmission matrices for a new, species 2, defect in a^(1)_3. 2. Folding, linking defects in simply laced theories to defects in non-simply laced theories. Folding is used in this thesis to find defects in the c^(1)_n, d^(2)_n and a^(2)_2n affine Toda field theories.