Kinetic plasma instabilities are important for regulating the temperature anisotropies of electronsand ions in solar wind. For the low beta regime, it is known that electromagnetic ion/electroncyclotron instabilities are important, but in the literature these unstable modes are discussed underthe assumption of parallel propagation. The present paper extends the analysis to two (or withcylindrical symmetry, three) dimensions. The analysis is further extended to include quasilineardescription with the assumption of the bi-Maxwellian velocity distribution function. Such an analysislays the foundation for an eventual study in which cyclotron instabilities as well as obliquelypropagating unstable modes such as the mirror instability are simultaneously taken into account.The present paper first lays down the basis for such future efforts in which the two- or threedimensional linear and quasilinear theories of cyclotron instabilities in the low beta regime areformulated.