Pieter Jacobus "Koos" Verdam was a Dutch politician of the defunct Anti-Revolutionary Party (ARP) now merged into the Christian Democratic Appeal (CDA).

The Zijlstra cabinet was the executive branch of the Dutch Government from 22 November 1966 until 5 April 1967. The cabinet was formed by the christian-democratic Catholic People's Party (KVP) and the Anti-Revolutionary Party (ARP) after the fall of the previous Cabinet Cals. The caretaker rump cabinet was a centrist coalition and had a minority in the House of Representatives with former Protestant Leader Jelle Zijlstra a former Minister of Finance serving as Prime Minister and dual served as Minister of Finance. Former Catholic Prime Minister Jan de Quay served as Deputy Prime Minister and Minister of Transport and Water Management, Protestant Leader Barend Biesheuvel continued as Deputy Prime Minister, Minister of Agriculture and Fisheries and the responsibility for Suriname and Netherlands Antilles Affairs from previous cabinet.