Jointless bridges, which have been constructed by several states, promote reduced maintenance costs, improved riding quality, lower impact loads, reduced snowplow damage to decks and approaches, and improved seismic resistance. In spite of many of these recognized benefits, the behavior of such structures is not yet fully understood, and nationally adopted criteria for their design are still lacking. This paper presents the results of an experimental and analytical research program, funded by the Federal Highway Administration, on the behavior of jointless and integral abutment bridges. The experimental work included testing and monitoring of bridge models and a bridge structure under construction, tests of bridge components; and a field survey of fifteen jointless bridges. Experimental results have resolved many questions regarding environmental effects, long-term and time dependent loading in combination with live and dead load effects. Results indicated that the live load continuity of the bridge can be reduced significantly with long-term and time dependent loading effects. In the analytical phase, the response of a jointless bridge was evaluated with respect to various design parameters. The research indicated that analysis procedures can be used to adequately quantify the structural response if accurate material and environmental parameters are known. However, in lieu of complex analyses, simplified design procedures are recommended.