American English has always preferred the punctuated spellings, Mr., Mrs., and Ms., treating the first two as abbreviations (from Mister and, although rarely spelled out, Missus). For the sake of consistency, Ms., though not an abbreviation, is also punctuated. British English does not treat these titles as abbreviations and leaves Mr, Mrs, and Ms unpunctuated.
Historically, Mrs. countered Mr. and was read as Mistress, the feminine of Mister, itself derived from master. Mrs. was originally used for both married and unmarried women but by the 1900s had become a title for only married women. Miss, which came to designate unmarried women, is a contraction of mistress and thus never punctuated.
The plural forms of Mr. and Mrs. take from the French Messieurs (Messrs.) and Mesdames (Mmes.). As with the singular titles, neither is punctated in British English.