We study two impediments to monetary policy transmission: (1) search friction in mortgage shopping (2) shadow banking. The first impediment weakens the mortgage refinancing channel of monetary policy. Many US mortgage borrowers do not refinance, despite seemingly having financial incentives to do so. We explore the role of search costs in explaining this inaction, focusing on the 2009-2015 period when mortgage rates declined. We estimate a dynamic discrete choice model of refinancing and search decisions using a panel data set, which includes information on the sequence of refinancing decisions and search intensity (the number of mortgage inquiries). We find that search costs significantly inhibit refinancing through two channels. First, hi...