Some recent theory in the area of rubberlike elasticity is illustrated by the analysis of strain-induced crystallization, chain entanglements in networks through constraint models, junction fluctuations and neutron scattering, and phase separations in oriented gels. Experimental techniques for characterizing elastomers involve the usual mechanical property measurements but also include chain orientation by birefringence measurements and infrared spectroscopy, small-angle neutron and X-ray scattering studies, pulse-propagation measurements, and Brillouin scattering. Some unusual types of elastomers described include (i) networks having known structures ("model" elastomers), (ii) networks having bimodal distributions of network chain lengths, (iii) reversibly cross-linked materials ("thermoplastic elastomers"), and (iv) elastomers cross linked in solution. Some novel approaches to reinforcement include (i) sol-gel-generated ceramic phases, (ii) rubbery particles for toughening ceramics, (iii) zeolites and other porous fillers that can be penetrated by network chains, and (iv) exfoliated clays. Examples of simulations involve the gelation process leading to network structures, non-Gaussian distributions, crystallization of elastomers that are chemically or stereochemically copolymeric, and reinforcement from particulate fillers.