A nice way of doing Except and Distinct: Original credit goes to: http://brendan.enrick.com/post/linq-your-collections-with-iequalitycomparer-and-lambda-expressions.aspx http://www.joe-stevens.com/2010/08/17/linq-lambda-expression-iequalitycomparer-for-ienumerable-distinct-and-except/

EnumerableExtensions.cs

public static class EnumerableExtensions
    {
        public static IEnumerable<TSource> Distinct<TSource>(this IEnumerable<TSource> enumerable, Func<TSource, TSource, bool> comparer)
        {
            return enumerable.Distinct(new LambdaComparer<TSource>(comparer));
        }

        public static IEnumerable<TSource> Except<TSource>(this IEnumerable<TSource> first, IEnumerable<TSource> second, Func<TSource, TSource, bool> comparer)
        {
            return first.Except(second, new LambdaComparer<TSource>(comparer));
        }
    }

LambdaComparer.cs

 public class LambdaComparer<T> : IEqualityComparer<T>
    {
        private readonly Func<T, T, bool> _lambdaComparer;
        private readonly Func<T, int> _lambdaHash;

        public LambdaComparer(Func<T, T, bool> lambdaComparer) :
            this(lambdaComparer, o => 0)
        {
        }

        public LambdaComparer(Func<T, T, bool> lambdaComparer, Func<T, int> lambdaHash)
        {
            if (lambdaComparer == null)
                throw new ArgumentNullException("lambdaComparer");
            if (lambdaHash == null)
                throw new ArgumentNullException("lambdaHash");

            _lambdaComparer = lambdaComparer;
            _lambdaHash = lambdaHash;
        }

        public bool Equals(T x, T y)
        {
            return _lambdaComparer(x, y);
        }

        public int GetHashCode(T obj)
        {
            return _lambdaHash(obj);
        }
    }

Usage.cs

List<Role> usersRoles = user.Roles.ToList();
List<Role> roles = new TestDbContext().Roles.ToList();
IEnumerable<Role> rolesUserIsNotIn = roles.Except(usersRoles, (role, role1) => role.Id == role1.Id);