Most of the family can be divided into three main branches: The first certain members of the clan were Aslak Jonsson and his wife, Lady Gro. The title of "Lady" suggests that she was previously married to a knight. Aslak was mentioned in 1443, when he willed his estate, including one-half of the Aspa farm to his daughter Jorann, who was married to Trond Toraldsson. They were the parents of the 25th Archbishop of Nidaros, :no:Olav Trondsson|Olav Trondsson. His brotherIvar Trondsson of Aspa inherited the farm from his mother. It is possible that he married to a woman from the Teiste family, the clan that might have produced Hans Bjørnsson Teiste, the 29th Bishop of Bergen. Olav and Ivar donated, in 1473, a large part of their lands, consisting a number of farms in Nordmøre, to the Nidaros Cathedral for a period of 30 years but a hundred years and several lawsuits would pass before the donation was returned to the Aspa family. On 11 September 1578 in Trondheim, the Herredag declared Ivar's grandson, Auden Tostensson of Aspa, the rightful heir to all the original Aspa properties of the Cathedral. Auden's daughter's son Auden Ågesson settled at Molde, as the owner of several farms, including :no:Reknes|Reknes. In other branches of the clan, the surname Trygge occurred later but its origins are uncertain. There is a prevailing theory among the Norwegian genealogists that Jorunn, the mother of the 28th and last Catholic Archbishop of Nidaros, Olav Engelbrektsson, might be from the Aslak Jonsson branch of the Aspa family as the daughter of Ivar Trondsson from Frei in Nordmøre, and the niece of Olav Trondsson, the 26th Archbishop. But, throughout the lives of Jorunn and her son, the records were more concerned with the church, the politics and the wars than with the families. So there may not be enough evidence to prove that Jorunn was the niece of Olav Trondsson and the mother of Olav Engelbrektsson as well as the sister of the 26th Archbishop of Nidaros :no:Gaute Ivarsson|Gaute Ivarsson, and the grandmother of Torbjørn Olavssøn Bratt, the first Lutheran "superintendent" of Trondheim. Engelbrektsson did help with the education and careers of Torbjørn and his brother, Jens Olavssøn Bratt, but their biographies at Norsk Biografisk Leksikon do not name him as their uncle and Jorunn as their grandmother.
Books (all in Norwegian">Norwegian language">Norwegian )
:no:Tore H. Vigerust|Tore Hermundsson Vigerust, editor, Aspa-seminaret : Sandvika 25 oktober 1996, Kristiansund 6–7 september 1997, in : Adelsprosjektets skrifter, bind 2 ,
Finn Oldervik, "Ouden Oudenson i Aspen – har han levd? Gaute Ivarson – var han likevel son til Ivar Trondson i Aspen? ", in : Jan H. Leithe and Hedvig Wist, editors, Årbok for Nordmøre 1998 , ISSN 0333-2152, pages 71–77
Anders Stølen, "Olav Engelbrektsson og Aspe=ætta : Resyme over synspunkt ,,
Ottar Roaldset, Gards- og ættesoge for Straumsnes, bind III ,, pages 438 ff.
Oddvar Grønli, "Ei ættetavla frå reformasjonstida ", Norsk Slektshistorisk Tidsskrift , Volume 13, Issue 2, pages 209–244
Arne I. Hoem, "Litt mer om Aspaslekten og slekten Hagerup ", Norsk Slektshistorisk Tidsskrift, Volume 25, pages 154-156
Magnus Mardal, "Aspaslekten - en nordmørsk stormannsslekt fra 1200-tallet ", Norsk Slektshistorisk Tidsskrift, Volume 32, pages 53–63
:no:Klaus Johan Myrvoll|Klaus Johan Grønseth Myrvoll, "Eitkvart nytt um Aspa-ætti ", Norsk Slektshistorisk Tidsskrift, Volume 36, Issue 4, pages 273-282
Klaus Johan Grønseth Myrvoll, "Margrete i Aspa – løysing på floken ", Norsk Slektshistorisk Tidsskrift, Volume 41, Issue 1, pages 42–63