Asymptotic Phase for Stochastic Oscillators The reduction of n-dimensional limit cycle dynamics to 1-dimensional phase dynamics provides a powerful tool for studying entrainment and synchronization of nonlinear oscillators. Two generalizations have been proposed to extend this reduction to stochastic oscillators. One extends the notion of isochrons (surfaces moving together in time) to surfaces with constant mean first passage times (MFPT) from one to the next (Schwabedal and Pikovsky 2013 Phys. Rev. Lett.). A second proposal identifies the phase as the complex argument of the eigenfunction of the adjoint Fokker-Planck operator associated with the slowest decaying complex eigenvalue (Thomas and Lindner 2014 Phys. Rev. Lett.). I will describe the latter notion of ``asymptotic phase" and discuss its relation to the phase based on the MFPT property.