This thesis analyzes the interrelation between market structure and price formation in credit derivatives markets. Traditionally, credit derivatives are traded in relatively opaque over-the-counter markets in which trading is segmented and subject to many imperfections from which illiquidity may arise. Recent regulatory reforms have brought transparency to some credit derivatives markets without affecting their segmented structures. The first chapter, which is joint work with Anders B. Trolle, analyzes whether liquidity risk is priced in the cross section of returns on credit default swaps (CDSs). The analysis is based on a factor pricing model and a tradable liquidity factor that is constructed from returns on index arbitrage strategies. The underlying presumption is that violations of simple no-arbitrage relations between different CDS contracts reflect constraints on the risk-bearing capacity of CDS market intermediaries and, in broad terms, CDS market illiquidity. The analysis reveals priced liquidity risk in that credit protection sellers earn higher expected excess returns on CDS contracts with higher liquidity exposures. The liquidity risk premium is significant and accounts for 24% of CDS spreads, on average. CDS risk premia correlate negatively with proxies for the risk-bearing capacity of CDS market intermediaries, which is consistent with intermediary frictions affecting the pricing of CDSs. The second chapter, which is joint work with Pierre Collin-Dufresne and Anders B. Trolle, analyzes transaction costs in the dealer-to-customer (D2C) and dealer-to-dealer (D2D) segments of the post-Dodd-Frank index CDS market. Dodd-Frank regulations that made all-to-all trading possible had the potential to break up the market's segmented structure but failed to do so. This led to a controversy with some market participants arguing that the segmented structure is optimal and other market participants arguing that dealers maintain the segmented structure in order to limit competition by alternative liquidity providers. The analysis reveals that D2C trades indeed have larger transaction costs than D2D trades but that the differences in transaction costs reflect differences in price impacts rather than differences in profits from liquidity provision. D2C trades are even competitive relative to executable bids and offers in the D2D segment, suggesting that the market structure delivers favorable prices for customers who value immediacy. The third chapter documents a decline of transaction costs and profits from liquidity provision in the index CDS market over a two-and-a-half-year period during which Dodd-Frank regulations were implemented. Transaction costs and profits from liquidity provision declined around the introduction of so-called swap execution facilities (SEFs); i.e., regulated trading platforms that offer pre-trade transparent methods of trade execution. Trades that are executed on SEFs have lower transaction costs and are less profitable from a liquidity provider's perspective in comparison to bilaterally negotiated trades, which is consistent with better comparison shopping and stronger price competition on SEFs. Dodd-Frank regulations mandating on-SEF trade execution that were implemented after the introduction of SEFs did not affect transaction costs and profits from liquidity provision, suggesting that there is no incremental effect associated with mandatory pre-trade transparency.