1. It belongs to System.Collections namespace.
2. IEnumerable is the best way to write query on collections data type like list,array etc.
3. IEnumerable is the return type for LINQ to object and LINQ to XML queries.
4. IEnumerable does not support lazy loading.So it's not recommended approach for paging scenarios.
5. It supports extension methods.
1. IQueryable belongs to System.Linq namespace.
2. IQueryable is the best way to write query on data like remote database,service collections etc.
3. IQueryable is the return type for LINQ to SQL queries.
4. IQueryable support lazy loading.So it can be used for paging scenarios.