  In this paper Janus black holes in AdS3 are considered. These are static
solutions of an Einstein-scalar system with broken translation symmetry along
the horizon. These solutions are dual to interface conformal field theories at
finite temperature. An approximate solution is first constructed using
perturbation theory around a planar BTZ black hole. Numerical and exact
solutions valid for all sets of parameters are then found and compared. Using
the exact solution the thermodynamics of the system is analyzed. The entropy
associated with the Janus black hole is calculated and it is found that the
entropy of the black Janus is the sum of the undeformed black hole entropy and
the entanglement entropy associated with the defect.
