getting type T from IEnumerable<T>

IEnumerable<T> myEnumerable;
Type type = myEnumerable.GetType().GetGenericArguments()[0]; 

Thusly,

IEnumerable<string> strings = new List<string>();
Console.WriteLine(strings.GetType().GetGenericArguments()[0]);

prints System.String.

See MSDN for Type.GetGenericArguments.

Edit: I believe this will address the concerns in the comments:

// returns an enumeration of T where o : IEnumerable<T>
public IEnumerable<Type> GetGenericIEnumerables(object o) {
    return o.GetType()
            .GetInterfaces()
            .Where(t => t.IsGenericType
                && t.GetGenericTypeDefinition() == typeof(IEnumerable<>))
            .Select(t => t.GetGenericArguments()[0]);
}

Some objects implement more than one generic IEnumerable so it is necessary to return an enumeration of them.

Edit: Although, I have to say, it's a terrible idea for a class to implement IEnumerable<T> for more than one T.

I'd just make an extension method. This worked with everything I threw at it.

public static Type GetItemType<T>(this IEnumerable<T> enumerable)
{
    return typeof(T);
}

I had a similar problem. The selected answer works for actual instances. In my case I had only a type (from a PropertyInfo).

The selected answer fails when the type itself is typeof(IEnumerable<T>) not an implementation of IEnumerable<T>.

For this case the following works:

public static Type GetAnyElementType(Type type)
{
   // Type is Array
   // short-circuit if you expect lots of arrays 
   if (type.IsArray)
      return type.GetElementType();

   // type is IEnumerable<T>;
   if (type.IsGenericType && type.GetGenericTypeDefinition() == typeof (IEnumerable<>))
      return type.GetGenericArguments()[0];

   // type implements/extends IEnumerable<T>;
   var enumType = type.GetInterfaces()
                           .Where(t => t.IsGenericType && 
                                  t.GetGenericTypeDefinition() == typeof(IEnumerable<>))
                           .Select(t => t.GenericTypeArguments[0]).FirstOrDefault();
   return enumType ?? type;
}