Differences in Bidding at MP vs IMPs

Matchpoints (MP) IMPs
Contract type NT first, majors next, minors last All types equal, seek the most comfortable makeable contract
Partscores Fiercely fought over Battles continue, but are toned down
Games/slams Bid moderately Aggressively bid, especially when vulnerable
Pre-emptive actions A widely used tactic Emphasised. Can create large swings
Sacrificing Aggressively pursued Need a clear-cut save; absolutely no phantom saves
Safety Plays Infrequent as overtricks are so important Frequent, as ensuring the contract is all important
Penalties Usually lots of leeway as only one board is involved if you misguess Bidding is sounder (especially red vs white) to avoid large penalties
Distributional hands Normal treatment Insure against big swings--bid one more in competitive auctions
Doubling Extensive, especially at partscore levels More limited; needs to be clearly your hand, a trump stack or misfit
Use of undiscussed conventions Can happen infrequently Avoid like the plague!

After Hall, Burt and Rose-Hall, Lynn (1966) How the experts win at bridge, Jordan Press.