A primer composition is provided for priming roofing and waterproofing membranes such as EPDM and TPO. The primer composition includes a halogenated copolymer of isobutylene and p-methyl styrene, a thermoplastic rubber, a tackifier, and a solvent comprising water and at least one volatile organic compound. The primer composition also preferably includes a plasticizer and an accelerator/cure package. The primer composition exhibits a volatile organic compound (VOC) content of less than about 250 g/l, and promotes effective adhesion of roofing adhesives to roofing membranes.