Petrus Josephus Mattheus "Piet" Aalberse Sr. (27 March 1871 – 5 July 1948) was a Dutch politician of the General League of Roman Catholic Caucuses, later the Roman Catholic State Party (RKSP) and later co-founder of the Catholic People's Party (KVP) and jurist. He was granted the honorary title of Minister of State on 31 December 1934.^[1]

Alberse applied at the Leiden University in June 1891, majoring in Law and obtaining a Bachelor of Laws degree in July 1893. He worked as a student researcher before graduating with a Master of Laws degree in July 1897. Aalberse worked as a lawyer in Leiden from August 1897 until April 1901. Aalberse also worked as editor of the Catholic newspapers De Tijd and the De Maasbode from November 1898 until 25 September 1918. Aalberse served on the municipal council of Leiden from September 1899 until September 1918, and served as an alderman in Leiden from September 1901 until February 1903. Aalberse became a member of the House of Representatives after the death of Herman Schaepman, serving from 24 February until 21 June 1916. Aalberse worked as a professor of Administrative law and Labour law at the Delft Institute of Technology from 21 June 1916 until 25 September 1918. After the 1918 general election, Aalberse was appointed as the first Minister of Labour in the first Ruijs de Beerenbrouck cabinet, taking office on 25 September 1918. After the 1922 general election Aalberse continued as Minister of Labour in the second Ruijs de Beerenbrouck cabinet, taking office on 18 September 1922. On 1 January 1923, the Ministry of Labour and the Ministry of Agriculture, Commerce and Industry were combined to form the Ministry of Labour, Commerce and Industry, with Aalberse continuing in the post as the newly renamed Minister of Labour, Commerce and Industry. After the 1925 general election, Aalberse was not given a cabinet post in the new cabinet, the Cabinet Ruijs de Beerenbrouck II was replaced by the Cabinet Colijn I on 4 August 1925. Aalberse subsequently returned to the House of Representatives as a frontbencher, taking office on 15 September 1925. After the leader of the Roman Catholic State Party and Parliamentary leader of the Roman Catholic State Party in the House of Representatives Willem Hubert Nolens announced his retirement from national politics, Charles Ruijs de Beerenbrouck was nominated as his successor as leader and Aalberse was selected as Parliamentary leader in the House of Representatives, taking office on 15 September 1931. After the leader of the Roman Catholic State Party Charles Ruijs de Beerenbrouck was elected as Speaker of the House of Representatives he subsequently stepped down as leader in favor of Aalberse on 31 May 1933.

On 21 July 1898, Aalberse married Elisabeth Johanna Maria Schmier, with whom he had seven daughters and one son. He was member of the "Raad der Vereniging" of De Nederlandsche Padvinders from 1936 till 1947.