Developmental editing looks at the book as a whole: its organization, pacing, focus and suitability for the intended reader. The editor may identify missing context, repeated ideas or chapters that need a different order. This work usually happens before detailed sentence-level editing.
Copyediting comes later, refining grammar, wording, consistency and style while preserving the author’s voice. Some projects need both services, while others need only one. Ask for a sample edit and a written scope so you understand exactly which stage your manuscript is ready for.