Then abbreviated TSE, the exchange opened in Toronto’s Masonic Hall in 1861 with 18 stocks listed. The Association of Brokers that created the TSE formed in 1852, but no official records of the Association’s business practices have survived. The Legislative Assembly of Ontario formally incorporated the exchange in 1878.

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The TSE thrived, increasing in size steadily except for one brief period in 1914. For three months that year the exchange shut down out of fear for a financial panic because of the onset of World War I. It took another leap in size in 1934 when it merged with the Standard Stock and Mining Exchange, its biggest competitor.
Throughout the twentieth century, the TSE has been eager to embrace technological innovations in the world of stock trading. For example, it introduced the Computer Assisted Trading System (CATS) in 1977, which was one of the first automated trading systems. In 1997, it switched from fractional trading to decimal trading, and in 1997, it closed its trading floor, making the transition to electronic trading.

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In 2008, a TSX (as it had been abbreviated since 2001) held a shareholders’ meeting and officially changed the name to TMX Group Inc. This was because of a realignment culminating in TSX’s acquisition in late 2007 of the Montreal Exchange for (C) $1.31 billion.