The Piano Trio was written in 1948 and can be justifiably labeled Kokkonen's opus 1. It is certainly the most substantive work he had written up to that point in his career—the prior decade consisted of only short piano works and miscellaneous songs—and the advance the trio represented over these earlier works, as regards pitch construction and formal design, undoubtedly allowed Kokkonen to enlarge his compositional thinking, a process of growth which led to the Piano Quintet a few years later, the composition widely considered to be the first major work from his oeuvre.