The Hays Code was a censorship and guideline body that regulated films created by major studios in the USA. In order to be allowed to be distributed, films must have attained a certificate from this (non-governmental) board to prove that they adhered to its strict censorship and regulations.
By the late 1950s, the power and enforcement of this board began to decline. In 1948, the US Supreme Court handed down its “Paramount Decision” which outlawed vertical integration of the major studios, allowing theaters to be independently owned. Independent theaters then began importing more foreign films as well as showcasing independent films made in the US. With these kinds of films being now shown to audiences at a larger scale, Hollywood-made Hays-Code bound films had trouble competing.
In its later years, the board relaxed its enforcement and by 1968, it was replaced by the MPAA Rating system.
Some films in this list may have been produced and released during this era, but may not have been subjected to the Hays Code due to being made independently or were made outside the United States.