This work in theoretical nuclear physics will study the properties of hadrons in hot dense matter as it is expected to occur in high energy heavy-ion collisions. The properties of mesons in matter will be studied using density dependent masses and coupling constants. The relativistic transport theory will also be generalized to include the density dependence of other hadrons. The long range goal of this work is to understand the dynamics of relativistic heavy-ion collisions such as will be produced in the future RHIC facility in search of the quark-gluon plasma.