Example fiber optic connector systems have rugged, robust designs that are environmentally sealed and that are relatively easy to install and uninstall in the field. Some connector systems can be configured in the field to be compatible with different styles of fiber optic adapters. Some connectors include a first seal (90) on a release sleeve; and a second seal (88) between the release sleeve and a connector body. Other connectors include a seal (139) and a flexible latch (136) on a connector. Other connectors include a protective structure (228, 328, 428) that mounts over the fiber optic connector. Other connectors include a protective outer shell (528, 860) and a sealing and attachment insert (570, 570A, 876). Other connectors include a protective outer shell (728) and a fastener (780).