Bartolomeo Giuseppe "del Gesù" Guarneri (21 August 1698, Cremona – 17 October 1744, Cremona), also known as Joseph Guarnerius del Gesu, is celebrated as one of the most significant Italian luthiers, often mentioned alongside Nicolò Amati (1596–1684) and Antonio Stradivari (1644–1737). The rare and exceptional tonal qualities of Del Gesu violins have made them some of the most valuable and sought-after instruments in the world today. Notably, his 1741 violin, the 'ex-Vieuxtemps,' achieved a record sale price exceeding £10.5 million ($16.4 million) in 2012–13.

Giuseppe was born into a notable family of luthiers, being the grandson of Andrea Guarneri (1626–1698) and the son of Giuseppe Filius Andreæ (1666–ca. 1740). He began his apprenticeship in the family workshop alongside his elder brother, Pietro Guarneri (1695–1762). The earliest surviving violins from Guarneri, dated around 1715–22, closely followed the Stradivari design with slight alterations, a bold and controversial decision within his family's traditional context. The Guarneri family faced a decline in reputation after Antonio Stradivari established his workshop in Cremona around 1680. While Giuseppe's grandfather, Andrea, adhered strictly to the "Grand Amati" style, Giuseppe and his brother sought greater creative freedom. Pietro moved to Venice around 1717, following their uncle Pietro 'di Mantova', while Giuseppe remained in Cremona, establishing his own workshop around 1726, competing against the family business for a decade. Despite this rivalry, the brothers maintained a close familial bond; Giuseppe returned to Casa Guarneri around 1731 to assist as his father's health declined.

The nickname del Gesù, which applies to both Guarneri and his instruments, stems from the il bollo del Gesù (the "Jesus stamp") that Cremonese scribes began using in the mid-1720s to differentiate between the similar Latin signatures of father and son. This label featured a cross of Jerusalem and the abbreviation IHS, representing "Iesus Hominem Salvator," or "Jesus the Savior" in Greek: Jo∫eph Guarnerius fecit Cremonȩ anno [i]17##[/i] ☩IHS.

Throughout his career, del Gesù adopted an increasingly experimental approach. His violins from 1737 to 1742 diverged significantly from the Stradivari model, showcasing a unique outline with a flatter back and top, possibly influenced by Brescian luthiers such as Da Salò. Guarneri prioritized achieving a warmer and more vibrant sound over visual aesthetics, contrasting with the meticulous craftsmanship favored by many Cremonese luthiers of his time. Some of his later instruments featured asymmetric F-holes, carved intuitively based on the specific vibrational characteristics of the wood. Over his relatively brief career, Guarneri crafted approximately 200 violins, two smaller violins (the 1740 'Fountaine' and the 1735 'Chardon'), and the 1731 'Messeas' cello, which bears an erroneous label from Giuseppe Filius Andreæ.

Guarneri passed away at the age of 46 and did not have any children. Unlike Stradivari, who received considerable acclaim during his lifetime, Guarneri's recognition came posthumously. His violins are distinguished by their darker, "robust" midrange sound, particularly in the 315 Hz–1.25 kHz range, where Stradivari's instruments typically excel in the 200–250 Hz band or above 1.6 kHz. The first prominent admirer of del Gesù violins was the Italian virtuoso Gaetano Pugnani (1731–1798), who extolled their sound in the mid-1750s, nearly three decades before Pugnani's pupil, Niccolò Paganini (1755–1824), began advocating for Stradivari. The esteemed violinist Niccolò Paganini (1782–1840) regarded his 1743 'il Cannone' as the most valuable violin, helping to solidify Guarneri's fame during his lifetime.

Notable 'del Gesù' Players - Ole Bull, played the "last" 1744 del Gesù - Jascha Heifetz, regarded his c.1740 violin as superior to several Strads - Yehudi Menuhin, played the 1742 'Lord Wilton' and 1741 ex-Vieuxtemps, preferring them over the 1714 'Soil' Stradivarius - Anne Akiko Meyers, has a lifelong loan of the 1741 'Vieuxtemps' from its current anonymous owner - Midori Goto, plays the 1731 'ex-Huberman' - Rachel Barton Pine, has played the 1742 'ex-Bazzini', ex-Soldat since 2002, on a lifetime loan from an anonymous owner - Other notable players include Joseph Joachim, Maud Powell, Zvi Zeitlin, Leonid Kogan, Isaac Stern, Pinchas Zukerman, Itzhak Perlman, Henryk Szeryng, Eugene Fodor, Nigel Kennedy, Henning Kraggerud, Gidon Kremer, Arve Tellefsen, Salvatore Accardo, Augustin Hadelich, Arthur Grumiaux, and many others.