If you have ever built a playlist, you already know a lot about the problem this chapter solves. Putting ten slow ballads back-to-back makes for a boring evening, just as filling a credit portfolio with only high-yield energy bonds leaves you dangerously exposed when oil prices fall. This chapter shows how to mix credit assets so that each holding pulls its weight, using mathematical tools that turn hunches into disciplined bets — and we will even learn how to blend your own market views with the market’s collective wisdom.