How does LINQ expression tree translation work internally?

Expression trees are parsed by LINQ providers to translate C# logic into query languages like SQL.

When you write IQueryable queries, C# does not execute delegates. Instead, it builds an expression tree (a structured representation of code). Providers like EF Core traverse this tree node-by-node, converting operations such as Where, Select, and Join into SQL AST equivalents. This allows database-side execution instead of in-memory filtering. If a node cannot be translated, it either throws or switches to client evaluation depending on configuration.