IEnumerable Vs IQueryable

	IEnumerable	IQueryable
Namespace	System.Collections Namespace	System.Linq Namespace
Derives from	No base interface	Derives from IEnumerable
Deferred Execution	Supported	Supported
Lazy Loading	Not Supported	Supported
How does it work	IEnumerable is suitable just for iterate through collection and you can not modify (Add or Remove) data IEnumerable bring ALL data from server to client then filter them, assume that you have a lot of records so IEnumerable puts overhead on your memory.	Whenever we encounter to huge data with so many records so we have to reduce overhead from application. IQueryable prepares high performance in such situations (huge data) by filtering data firstly and then sending filtered data to client.
Suitable for	LINQ to Object and LINQ to XML queries.	LINQ to SQL queries.
Custom Query	Doesn’t supports.	Supports using CreateQuery and Execute methods.
Extension mehtod parameter	Extension methods supported in IEnumerable takes functional objects.	Extension methods supported in IEnumerable takes expression objects i.e. expression tree.
When to use	when querying data from in-memory collections like List, Array etc.	when querying data from out-memory (like remote database, service) collections.
Best Uses	In-memory traversal	Paging

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