In this paper, we discuss the basic properties of the electromagnetic waves guided by waveguides involving indefinite media. For the sake of simplicity, we assume that the and tensors are simultaneously diagonalizable. We present a detailed study about the modes propagating in several types of waveguides filled with indefinite media, namely, planar and rectangular cross section waveguides, including the indefinite-medium H-guide. The respective modal equations are derived and the conditions under which the modes are guided are investigated. Compared with the conventional anisotropic waveguides, several uncommon properties are demonstrated, including the coexistence of forward and backward modes and the propagation of super-slow modes.