Going from IQueryable> to IEnumerable I have a "GetPersonsPerDepartment()" method returning a IQueryable&lt;IEnumerable&lt;Person&gt;&gt; while I'm trying to get a simple List&lt;Person&gt; or IEnumerable&lt;Person&gt; with all the persons from every department. I wrote a simple method GetAllPersons() that solves this with a loop but I feel I must be missing a simple command to get the same result: 

private List&lt;Person&gt; GetAllPersons()
{
    List&lt;Person&gt; allPersons = new List&lt;Person&gt;();

    foreach(var Persons in GetPersonsPerDepartment())
    {
        allPersons.AddRange(Persons);
    }

    return allPersons;
}

private IQueryable&lt;IEnumerable&lt;Person&gt;&gt; GetPersonsPerDepartment()
{
    IQueryable&lt;IEnumerable&lt;Person&gt;&gt; Persons;

    using (var context = MySource.GetPersonsContext())
    {
        var library = "Personlist";
        var PersonFolderList = context.Web.Lists.GetByTitle(library);
        context.Load&lt;List&gt;(PersonFolderList);

        var PersonFolderListItems = PersonFolderList.GetItems(new CamlQuery());
        context.Load&lt;ListItemCollection&gt;(PersonFolderListItems);

        context.ExecuteQuery();

        Persons = PersonFolderListItems.Where(x =&gt; x.FileSystemObjectType == FileSystemObjectType.Folder).Select(x =&gt; GetPersonsFromFolderListItem(x, context, PersonFolderList));
    }

    return Persons;
}
Use SelectMany. As in, allPersons.SelectMany(s =&gt; s);. This flattens the sequence for you.