Bridges are similar to routers in some ways, but different in others. Bridges connect two LAN segments together, whether they are the same or different architectures, i.e. an ethernet to an IPX/SPX (Novell) network segment.
They work in the data link layer (2nd layer) of the seven-layer OSI TCP/IP model. Routers work in the network layer (3rd layer) of the OSI model. Bridges are faster than routers because bridges don't have to "read" the protocol to retrieve the routing tables. In other words, you can use a bridge to connect to LAN segments that use non-routable protocols, such as NetBIOS or NetBEUI, because a bridge doesn't need or use routing tables. A switch is an example of a bridge.