public class GroupElement : Element, ArcGIS.Desktop.Mapping.IElement, ArcGIS.Desktop.Mapping.IElementContainer, System.ComponentModel.INotifyPropertyChanged, System.IComparable, System.IDisposable, System.IEquatable<Element>  

{
  //Create an empty group element at the root level of the contents pane
  //Note: Must be on QueuedTask.Run

  //container is IElementContainer - GroupLayer or Layout
  GroupElement grp1 = ElementFactory.Instance.CreateGroupElement(
                        layout, null, "Group");
  // *** or ***
  //Create a group element inside another group element

  //Find an existing group element
  //container is IElementContainer - GroupLayer or Layout
  GroupElement existingGroup = layout.FindElement("Group") as GroupElement;

  //Create on worker thread
  GroupElement grp2 = ElementFactory.Instance.CreateGroupElement(
      existingGroup, null, "Group in Group");
}

{
  //Create a group with a list of elements at the root level of the contents pane.

  //Find an existing elements
  //container is IElementContainer - GroupLayer or Layout
  var elem1 = layout.FindElement("Polygon 1");
  var elem2 = layout.FindElement("Bezier Text");
  var elem3 = layout.FindElement("Cloud Shape 2");

  //Construct a list and add the elements
  var elmList = new List<Element>
  {
    elem1,
    elem2,
    elem3
  };
  //Note: Must be on QueuedTask.Run

  GroupElement groupWithListOfElementsAtRoot =
            ElementFactory.Instance.CreateGroupElement(
                     layout, elmList, "Group with list of elements at root");
  // *** or ***

  //Create a group using a list of element names at the root level of the contents pane.

  //List of element names
  var elmNameList = new[] { "Para Text1", "Line 3" };

  //Note: Must be on QueuedTask.Run

  var elemToGroup = layout.FindElements(elmNameList);
  GroupElement groupWithListOfElementNamesAtRoot =
        ElementFactory.Instance.CreateGroupElement(
             layout, elemToGroup, "Group with list of element names at root");
}