A portable shelter includes a frame structure with a plurality of pole structures. In some embodiments, a pole structure includes telescopically movable pole portions and a spring-biasing mechanism configured to bias one pole portion away from the other. In some embodiments, a center hub structure of the portable shelter includes a locking mechanism for engaging one of the pole portions to interfere with telescopic movement of the pole structure. In some embodiments, a pole structure includes a flexible portion attached to a first rigid portion, and a second rigid portion that is movable relative to the first rigid portion. The second rigid portion is pivotable or telescopically movable between a first position in which the second rigid portion overlaps the first rigid portion such that the flexible portion is free to flex, and a second position in which the second rigid portion overlaps and restrains the flexible portion.