This thesis deals with the music group Extempore since its foundation by Jaroslav Jeronym Neduha in 1973 until its annulment by Mikolas Chadima in 1981. The thesis shows the important moments of the group and its members. Jaroslav Jeronym Neduha was Extempore's frontman by the year 1979 then he left the group and its management handed to Mikolas Chadima. Both gave to Extempore its characteristic style in the musical aspect, lyrics and performance. Extempore gained lots of fans, so the State Security focused on them as a obnoxius music group. The thesis has the aim to reveal Extempore's role in Czech musical underground. Firstly I defined alternative culture in relation to underground and official culture with focus to the music. Also I described Prague's unofficial big beat scene between 1973 - 1981. Primarily the thesis is focused on alternative music scene and musical underground. The review also contains other noncommercial movements during that time - folk association Safran and younger musical movement New Wave that inspirated Chadima's Extempore. Since the 1979 Extempore has been more and more pressed to the illegality until they got ban to perform their music in any Prague's club. Anyways they pushed for public performances and they kept up in free creation. An important outcome is fact that...