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The following is a partial list of IBM precursors, acquisitions and spinoffs. IBM has undergone a large number of mergers and acquisitions during a corporate history lasting over a century; the company has also produced a number of spinoffs during that time.

The acquisition date listed is the date of the agreement between IBM and the subject of the acquisition. The value of each acquisition is listed in USD because IBM is based in the United States. If the value of an acquisition is not listed, then it is undisclosed.

Since the 1960s or earlier, IBM has described its formation as a merger of three companies: The Tabulating Machine Company (1880s origin in Washington, DC), the International Time Recording Company (ITR; 1900, Endicott), and the Computing Scale Company of America (1901, Dayton, Ohio). However, there was no merger, it was an amalgamation, and an amalgamation of four, not three, companies. The 1911 CTR prospectus states that the Bundy Manufacturing Company was also included. While ITR had acquired its time recording business in 1900 Bundy had remained a separate entity producing an adding machine and other wares.

CTR owned the stock of the four companies; CTR neither produced nor sold any product; the four companies continued to operate, as before, under their own names. CTR was renamed "IBM" in 1924. The separate companies were integrated in 1933 and the holding company eliminated.

Number of acquisitions per year according to table below:

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