Despite Power Query offering over 700 built-in functions, there are instances where creating custom functions is necessary. There were many situations in the previous chapters where you used custom functions, such as using the fifth argument of Table.Group() in Chapter 6 , Example 7 in Chapter 7 , Example 5 in Chapter 8 , and using the third arguments of List.Accumulate() and List.Generate() in Chapter 9 . In this chapter, you learn more about custom functions in Power Query.