New generation theorems for singular kinetic equations in L 1 -spaces are given. We show that space homogeneous linear kinetic equations in L 1 spaces and full transport equations with advection termv. ∂ ∂ x in L 1 spaces on arbitrary spatial domains share several generation properties. In particular, in the subcritical case, they share the so-called "closure property" of the generator. We also show, for subcritical equations, that a principle of detailed balance insures this "closure property". We show, in the subcritical case, that the full transport operator in bounded geometries is always a generator for sublinear collision frequencies. We provide also generation theorems based on (weak) compactness methods and, in the case of space homogeneous kinetic equations, study the essential spectrum of the corresponding semigroup. The diffusion models (used in nuclear reactor theory) where the advection operator v. ∂ ∂ x is replaced by a Laplacian operator in space variable are also dealt with.