Jozef Maria Laurens Theo "Jo" Cals (18 July 1914 – 30 December 1971) was a Dutch politician of the Catholic People's Party (KVP) and jurist who served as Prime Minister of the Netherlands from 14 April 1965 until 22 November 1966.

Cals became a member of the House of Representatives shortly after 1948 general election taking office on 19 August 1948 serving as a frontbencher and spokesperson for education and social work.

After the 1952 general election, Cals was appointed as Minister of Education, Arts and Sciences in the second Drees cabinet, taking office on 2 September 1952.

Cals also became active in the public sector as a non-profit director and served on several state commissions and councils on behalf of the government.

Cals left office upon the installation of the caretaker Zijlstra cabinet on 22 November 1966 and announced his retirement.

He holds the distinction of as the fourth longest-serving cabinet member since 1850 with 14 years and 353 days and his premiership is consistently considered both by scholars and the public to have been average.

He became Minister of Education, Arts and Sciences serving from 2 September 1952 until 24 July 1963 in the cabinets Drees II and III, Beel II and De Quay, he helped pass the Mammoetwet, a law that transformed secondary education.

In the aftermath of the collapse of the Marijnen cabinet, Cals became Prime Minister of the Netherlands on 14 April 1965.

Cals was a hard worker but this was at the expense of his health, he died from a brain tumor in the MCH Westeinde hospital in The Hague on 30 December 1971 at the age of 57.