  We develop a general approach to finding combinatorial models for cluster
algebras. The approach is to construct a labeled graph called a framework. When
a framework is constructed with certain properties, the result is a model
incorporating information about exchange matrices, principal coefficients,
g-vectors, and g-vector fans. The idea behind frameworks arises from Cambrian
combinatorics and sortable elements, and in this paper, we use sortable
elements to construct a framework for any cluster algebra with an acyclic
initial exchange matrix. This Cambrian framework yields a model of the entire
exchange graph when the cluster algebra is of finite type. Outside of finite
type, the Cambrian framework models only part of the exchange graph. In a
forthcoming paper, we extend the Cambrian construction to produce a complete
framework for a cluster algebra whose associated Cartan matrix is of affine
type.
