Joannes Baptista Guadagnini, a.k.a. J. B. Guadagnini, (1711 - 1786), was one of the greatest luthiers (makers of violins and other string instruments in history. His instruments are often referred to as "poor man's Strads" which alludes to the work of Antonio Stradivari, who is generally considered to be the greatest violin maker of all time. Guadagnini made violins from about 1729 until his death and his work is divided into four main periods corresponding to and named after the four cities in Italy where he lived and worked: Parma, Piacenza, Milan, and Turin. Of these, the instruments from his last period, Turin, are generally the best and most valuable. In fact, the a.k.a. given above, "poor man's Strad", hardly seems applicable in modern times now that some of his instruments have reached sale prices as high as one million dollars. Nevertheless, with sales of Stradivari's violins occasionally topping five million dollars, the comparison is still valid.

Other prominent makers of the Guadagnini family include Giovanni's father, Lorenzo, his son, Giuseppe, and several lesser makers, as some of his descendants continued in the line of violin making through several generations. Of these, Lorenzo is considered the second best and Giuseppe is the third.

The German violinist Willy Hess was an owner of a Guadagnini.