  This is the first in a series of two papers. We use the Schwinger-Keldysh
formalism to derive semiclassical Boltzmann transport equations for massive
chiral fermions and scalar particles. Our considerations include complex mass
terms and mixing fermion and scalar fields, such that CP-violation is naturally
included, rendering the equations particularly suitable for studies of
baryogenesis at a first order electroweak phase transition. In part II we
discuss the collision terms.
