The Primera Categoría Serie B, shortened to Serie B or Primera B, is a professional football league in Ecuador. It is in the second tier of the Ecuadorian football league system. Contested by twelve clubs, it operates a system of promotion and relegation with the top-flight Serie A and the bottom-level Segunda Categoría. The season runs from February to December in two stages. For sponsorship reasons, it is known as the Copa Pilsener Serie B.
The Serie B has been in place since 1971 and has been held on a yearly basis since (except 1973 and 1983–88), often holding two tournaments a year. The top team at the end of the tournament is not called the champion, but rather the winner. The number of teams being promoted or relegated changed through the years because, like the Serie A, the format often changes on a seasonal basis. The 2010 season was split into two stages, each with an identical double round-robin format. The team with the most points at the end of both stages is the winner. The winner and runner-up both get promoted to the Serie A for the following season while the two teams with the fewest points at the end of the season are relegated to the Segunda Categoría.
Thirty different clubs have won the Serie B, but only twelve have won it multiple times. The most successful teams are LDU Portoviejo and Técnico Universitario, with five titles each. The current winner is C.S.D. Macará, who won their fourth title in 2016.
There are currently twelve teams in the 2017 Serie B.