Nesi, Nesis or NESI may refer to:

• NESI (Net-centric Enterprised Solutions for Interoperability), a joint effort between the US Navy and USAF
• Northeast Snowfall Impact Scale (NESIS), created to measure snowstorms in the US Northeast
• New Zealand eScience Infrastructure (NeSI), a specialised platform of shared high performance computing

• Nasi (mummy) [ca; es; it], a mummy in Biblioteca Museu Víctor Balaguer
• Giovanni Nesi (1456–1506), Florentine philosopher
• Nerio Nesi (1925–2024), Italian politician, businessman and banker
• Giovanni Nesi (born 1986), Italian pianist and professor of academic music
• Alexander Nesis (born 1962), founder, president and CEO of the ICT Group, a private equity firm headquartered in Moscow
• Luiz Ferreira Nesi, Brazilian footballer

• Nesi, a 2009 Indian Tamil film
• the ancient Roman port of Nesis, now called Nisida

• Nessie, the Loch Ness Monster, in Scottish folklore
• Nasi (Hebrew title)
• Nes (disambiguation)