Poisson structures of divisor-type are those whose degeneracy can be captured by a divisor ideal, which is a locally principal ideal sheaf with nowhere-dense quotient support. This is a large class of Poisson structures which includes all generically-nondegenerate Poisson structures, such as log-, b k -, elliptic, elliptic-log, and scattering Poisson structures.Divisor ideals are used to define almost-injective Lie algebroids of derivations preserving them, to which these Poisson structures can be lifted, often nondegenerately so. The resulting symplectic Lie algebroids can be studied using tools from symplectic geometry. In this paper we develop an effective framework for the study of Poisson structures of divisor-type (also called almost-regular Poisson structures) and their Lie algebroids. We provide lifting criteria for such Poisson structures, develop the language of divisors on smooth manifolds, and discuss residue maps to extract information from Lie algebroid forms along their degeneraci loci. Contents 1. Introduction 1 2. Divisors on smooth manifolds 5 3. Lie algebroids of divisor-type 8 4. Poisson structures of divisor-type 25 5. Residue maps and the modular foliation 39 References 55 2010 Mathematics Subject Classification. 53D17. 1 2 RALPH L. KLAASSEwe develop a framework for the study of Poisson structures of divisor-type. Below we outline the ideas underlying this framework, and mention our main results.The techniques and language developed in this paper are used to various establish results for almost-regular Poisson structures, including the computation of Poisson cohomology [32], determining the adjoint symplectic groupoids integrating them [33], and developing topological obstructions to their existence [31]. Moreover, this framework was used in [10] in the development of Gompf-Thurston methods for symplectic Lie algebroids.Poisson structures of divisor-type. In this paper we adapt the language of divisors to the context of smooth manifolds, following their use in [10,12]. A divisor consist of a line bundle together with a section whose zero set is nowhere dense. Each such pair (L, s) specifies a divisor ideal I s ∶= s(Γ(L * )) ⊆ C ∞ (X). Abstractly, divisor ideals are locally principal ideals I for which the support Z(I) ⊆ X of the quotient sheaf C ∞ (X) I is nowhere dense, whereThese ideals keep track of degenerative behavior along this support, and are an extension of the concept of a Cartier divisor in algebraic and complex geometry to the smooth setting.Poisson structures naturally lead to divisors: Given π ∈ Poiss(X) such that dim(X) = 2n, consider its Pfaffian ∧ n π ∈ Γ(det(T X)). Note that π is nondegenerate exactly at those points x ∈ X where ∧ n π x ≠ 0. Thus π is generically nondegenerate if and only if the pair (det(T X), ∧ n π) is a divisor. In this case we denote this pair by div(π), with associated divisor ideal I π ⊆ C ∞ (X). This ideal captures the behavior of π along Z(π) = Z(I π ), called the degeneracy locus of π, consisting of points where the rank of π is not maximal.In gen...