Example
ClientContext clientContext = new ClientContext("http://MyServer/sites/MySiteCollection");
GroupCollection collGroup = clientContext.Web.SiteGroups;
Group oGroup = collGroup.GetById(7);
UserCollection collUser = oGroup.Users;
clientContext.Load(collUser,
users => users.Include(
user => user.Title,
user => user.LoginName,
user => user.Email));
clientContext.ExecuteQuery();
foreach (User oUser in collUser)
{
Console.WriteLine("User: {0} Login name: {1} Email: {2}",
oUser.Title, oUser.LoginName, oUser.Email);
}