Title: An analytical approach to codimension-2 sliding bifurcations in the dry friction oscillator Authors: M. Guardia, S. J. Hogan, T. M. Seara July 31, 2009 Abstract: In this paper, we consider analytically sliding bifurcations of periodic orbits in the dry friction oscillator. The system depends on two parameters; $F$, which corresponds to the intensity of the friction and $\omega$, the frequency of the forcing. We prove the existence of infinitely many codimension-2 bifurcation points and we focus our attention on two of them; $A_1 := (\omega^{-1}, F) = (2, 1/3)$ and $B_1 := (\omega^{-1}, F) = (3, 0)$. We derive analytic expressions in $(\omega^{-1}, F)$ parameter space for the codimension-1 bifurcation curves that emanate from $A_1$ and $B_1$. We show excellent agreement with the numerical calculations of Kowalczyk and Piiroinen [KP08]. Keywords: Filippov systems, periodic orbits, sliding bifurcations, codimension-2 points. AMS classification scheme numbers: 37G15, 34A36, 34C25, 34C23.