this book presents the analytic-bilinear approach to integrable hierarchies, which gives a consistent and technically simple description of integrable hierarchies, and shows an easy and direct way to understand rather complicated structures, using mostly standard complex analysis. the language of the analytic-bilinear approach is suitable for applications to integrable nonlinear pdes, integrable nonlinear discrete equations, and for the applications of integrable systems to continuous and discrete geometry. this approach allows the representation of generalised hierarchies of integrable equations in a condensed form of finite functional equations, incorporating basic hierarchy, modified hierarchy, singularity manifold equation hierarchy and corresponding linear problems, which arise both in the compact discrete form and in the form of nonlinear partial differential equations. different levels of generalised hierarchy are connected via invariants of combescure symmetry transformation. the resolution of functional equations also leads to the tau-function and its additional formulae. audience: this book will be of interest to students and specialists whose work involves the theory of integrable systems, mathematical physics, topological groups, lie groups, finite differences, functional equations, partial differential equations and functions of a complex variable.