The following tables list the largest mergers and acquisitions by decade of transaction. Transaction values are given in the US dollar value for the year of the merger, adjusted for inflation. As of  2024[ [update]], the largest ever acquisition was the 1999 takeover of Mannesmann by Vodafone Airtouch plc at $183 billion ($ billion adjusted for inflation). AT&amp;T appears in these lists the most times with five entries, for a combined transaction value of $311.4 billion. Mergers and acquisitions are notated with the year the transaction was initiated, not necessarily completed. Mergers are shown as the market value of the combined entities.
Free market enterprises.
1870s.
Top 2 M&amp;A deals worldwide by value from 1870 to 1879:
1880s.
Top 2 M&amp;A deals worldwide by value from 1880 to 1889:
1890s.
Top 2 M&amp;A deals worldwide by value from 1890 to 1899:
1900s.
Top 3 M&amp;A deals worldwide by value from 1900 to 1909:
1910s.
Top 3 M&amp;A deals worldwide by value from 1910 to 1919:
1920s.
Top 5 M&amp;A deals worldwide by value from 1920 to 1929:
1930s.
Top 5 M&amp;A deals worldwide by value from 1930 to 1939:
1940s.
Top 5 M&amp;A deals worldwide by value from 1940 to 1949:
1950s.
Top 10 M&amp;A deals worldwide by value from 1950 to 1959:
1960s.
Top 10 M&amp;A deals worldwide by value from 1960 to 1969:
1970s.
Top 15 M&amp;A deals worldwide by value from 1970 to 1979:
1980s.
Top 30 M&amp;A deals worldwide by value from 1980 to 1989:
 ;templatestyles src="template:sticky header/styles.css"/ ;
1990s.
Top M&amp;A deals worldwide by value ($20 billion or larger) from 1990 to 1999:
 ;templatestyles src="template:sticky header/styles.css"/ ;
2000s.
Top M&amp;A deals worldwide by value ($20 billion or larger) from 2000 to 2009:
 ;templatestyles src="template:sticky header/styles.css"/ ;
2010s.
Top M&amp;A deals worldwide by value ($20 billion or larger) from 2010 to 2019:
 ;templatestyles src="template:sticky header/styles.css"/ ;
2020s.
Top M&amp;A deals worldwide by value ($20 billion or larger) from 2020 to 2029:
 ;templatestyles src="template:sticky header/styles.css"/ ;
State-owned enterprises.
Top M&amp;A deals worldwide by value ($20 billion or larger) between state-owned enterprises:
 ;templatestyles src="template:sticky header/styles.css"/ ;
Largest ever deals which have failed to complete.
This lists catalogues M&amp;A deals ($20 billion or larger in transaction value) which were confirmed, but for a number of reasons, failed to complete.
 ;templatestyles src="template:sticky header/styles.css"/ ;
References.
 ;templatestyles src="Reflist/styles.css" / ;