This chapter will be concerned with prepositional relatives that involve doubled and intrusive prepositions, and with evaluating a number of different accounts of these. I begin by looking at preposition doubling, outlining and evaluating two alternative syntactic analyses (a copying account in §3.2, and a splitting account in §3.3) before going on to investigate intrusive prepositions in §3.4. I then turn to present and evaluate a sociolinguistic account of preposition doubling in terms of hypercorrection in §3.5, before going on to look at processing accounts of preposition doubling and intrusion in §3.6 and presenting experimental evidence. I conclude the chapter with a brief summary of my main findings in §3.7.