Summary form only given. Photonic crystals have inspired a lot of interest recently due to their potential for controlling the propagation of light. Photonic crystals with line defects can be used for guiding light. A conventional method for making a two-dimensional (2D) dielectric-core photonic crystal (or PBG) waveguide is to remove one row of air columns. This usually results in a multimode waveguide. We present a more systematic way of making single-mode dielectric-core 2D PBG waveguides. It was recently shown that the main guiding mechanisms in dielectric-core PBG waveguides are total internal reflection and distributed Bragg reflection (DBR). The confinement of the guided mode in the center slab of the waveguide suggests that the properties of such modes can be modified by modifying the guiding structure in the vicinity of the center slab.