McCarthyism was a period in American history that saw U.S. Senator Joseph McCarthy of Wisconsin produce a series of investigations and hearings during the 1950s in an effort to expose supposed communist infiltration of various areas of the U.S. government. The term "McCarthyism" has since become a byname for defamation of character or reputation by means of widely publicized indiscriminate allegations, especially on the basis of unsubstantiated charges. Key facts about McCarthyism include:

• Origins: President Harry S. Trumans Executive Order 9835 of March 21, 1947, required that all federal civil-service employees be screened for "loyalty".

• Accusations: McCarthy claimed to have a list of members of the Communist Party USA working in the State Department, which attracted substantial press attention. He accused many people of being communists or communist sympathizers, often without evidence.

• Investigations: The most notable examples of McCarthyism include the investigations of alleged communists that were conducted by Senator McCarthy, and the hearings conducted by the House Un-American Activities Committee (HUAC) .

• Impact: McCarthyism destroyed thousands of lives and created a climate of fear and suspicion across the country. Many people lost their jobs or were blacklisted from working in their chosen professions.

Today, McCarthyism is synonymous with any perceived government activity that suppresses unfavorable political or social views by limiting or undermining vital civil rights and liberties under the pretext of maintaining national security.