This idiom challenges someone to back up their words, claims, or promises with tangible action or financial commitment, as if proving their sincerity by investing money where their boasts lie. It conveys a demand for proof of conviction or credibility, often used in competitive, professional, or social contexts to call out empty talk or urge follow-through. The phrase carries a tone of confrontation, challenge, or encouragement, reflecting cultural values of accountability and the human tendency to overpromise without delivering. It resonates in situations where rhetoric meets reality, capturing the pressure to demonstrate substance, and its financial imagery adds a layer of bold, practical stakes, evoking a bet or investment. The idiom often implies skepticism about someone’s intentions, making it a sharp expression for testing sincerity or commitment.

The phrase likely originated in late 19th-century America, rooted in gambling or business culture, where ‘putting money’ on a claim was a literal test of confidence, as seen in poker or speculative markets. Its earliest recorded use appears in an 1891 *Chicago Tribune* article, urging a politician to ‘put his money where his mouth is’ on a policy promise. The idiom gained traction in the early 20th century, reflecting America’s entrepreneurial and confrontational ethos, as seen in Sinclair Lewis’ *Babbitt* (1922), which critiques hollow boasts. Its use was amplified during the 1920s’ economic boom and later in political and media discourse, notably in *The New York Times* during the 1930s. The phrase’s adoption in British and Commonwealth English came through American media and business influence, particularly post-1940s, and its spread was fueled by its vivid imagery, evoking a financial wager, and its applicability to accountability, ensuring its enduring use across English-speaking cultures, from boardroom challenges to barroom bets.