Only two bertsolaris are needed to have a bertso session. Historically, bertsolaris would 'attack' with their versos whenever the occasion seemed right. Impromptu sessions would arise, with no rehearsal whatsoever. On one occasion, when Pello Errota was in the middle of reciting his bersos, Txirrita went over to listen. When Pello saw him, he improvised a berso, and Txirrita was quick to respond.
Ari naizela, ari naizela
hor ikusten det Txirrita.
Eta zein ez da harrituko gaur
gizon hori ikusita?
Dudarik gabe egina dio
oso dotore etorri zaigu
bi alkandora jantzita.
Hauxen da lotsa eman didana
gizon artera sartuta,
edozer gauza esaten degu
edan tantokin poztuta.
Bi alkandora ekarri ditut
bat eraztia ahaztuta.
Pellok bi nola jantziko ditu,
bat besterikan ez du-ta.
There was a period in which challenges or wagering on who was the best was quite common. Today, however, the following types of berso sessions are the most prevalent:
Among friends: a gathering of bersos around a dinner or lunch table. Bersolaris perform at their own free will, creating their own topics based on what they have heard or seen in their immediate surroundings. Session of this type are the most frequent.
Public square unstructured sessions: In these sessions, two to three bersolaris do their own thing in public squares and on feast days.
Festivals: Four or more bersolaris take part in these sessions. There is a person in charge of choosing the topics, deciding which bersolari will sing which topic and of generally directing the session.
Programmed sessions: These sessions are part of a programmed event: tributes, weddings, etc.
Others: These sessions clearly show bersolarismo's continual renovation process. Although they are not very widespread these alternative sessions are a reflection of how bersolarismo keeps up with the times: subject matter, musical sessions, experimental and education sessions, compound bersos and so on.
The Xenpelar Centre for Documentation connected to Bertsolari Elkartea (Association of Bersolari Enthusiasts) registered 1113 berso sessions in 1999.