We describe an algebraic chain level construction that models the passage from an arbitrary topological space to its free loop space. The input of the construction is a categorical coalgebra, i.e., a curved coalgebra satisfying certain properties, and the output is a chain complex. The construction is a modified version of the co-Hochschild complex of a differential graded (dg) coalgebra. When applied to the chains on an arbitrary simplicial set
X
X
, appropriately interpreted, it yields a chain complex that is naturally quasi-isomorphic to the singular chains on the free loop space of the geometric realization of
X
X
. We relate this construction to a twisted tensor product model for the free loop space constructed using the adjoint action of a dg Hopf algebra model for the based loop space.