The chapter is concerned with regularities that occur in texts, in particular repetitions and symmetries. They have a strong influence on the efficiency of algorithms. The central topic is the notion of repetition of factors: squares, cubes, maximal periodicities or runs, and overlaps. Problems deal with discovering or counting of repetitions. The related algorithms are usually short but tricky. Especially problems about runs are non-trivial but show the unexpected power of combinatorics of Lyndon words. Repetitions in labeled trees are also considered. Besides repetitions some problems deal with symmetrical words (palindromes) and anti-power words.