This monograph gives a detailed introductory exposition of research results for various models, mostly two-dimensional, of directed walks, interfaces, wetting, surface adsorption (of polymers), stacks, compact clusters (lattice animals), etc. The unifying feature of these models is that in most cases they can be solved analytically. The methods used include transfer matrices, generating functions, recurrence relations, and difference equations, and in some cases involve utilization of less familiar mathematical techniques such as continued fractions and q-series. The authors emphasize an...