Systems and methods for delivering release materials, for example drugs and other bioactive materials. Crystalline polymeric systems, referred to as CYC carriers, are associated with the release materials, through chemical bonding or through physical association. The crystallinity of the CYC carriers results from the presence of crystallizable side chains, for example long chain n-alkyl moieties, which results in relatively low and sharp melting temperatures. One class of CYC carriers, referred to as CYSC polymers, have a majority of the crystallizable side chains pendant from the polymer backbone. Another class of CYC carriers referred to as ECC polymers, have a majority of the crystallizable side chains attached to terminal units of the polymer backbone. The ECC polymers can for example be obtained by modification of PLGA polymers. The CYC carriers in another class of non-polymeric. Some CYC carriers, referred to as CYC assemblies, have enhanced crystallinity as a result of the physical association of crystallizable moieties which are present in different types of molecule, for example between a polymer containing crystallizable moieties and a monomer containing crystallizable moieties. For some uses, particularly the delivery of drugs, a bioerodable CYC carrier is preferably used.