Black Caps selector Gavin Larsen said the limited number of changes was representative of the consistent approach to selection.
"We've built a strong group of core players over the past couple of years and that's been a key factor to the consistency of the team's performance," Larsen said.
"When we've brought new players into the group, we've been really happy with how they've adapted and performed on the international stage.
Henry and George have made bright starts to their Black Caps careers and we look forward to watching their ongoing development.
"After missing out last year, Ish and Colin have both worked extremely hard on their game, as we saw with their performances for us in the shorter formats this summer. They thoroughly deserve their contracts."
A set criteria is used to rank players across all three forms of the game. Tests receive twice the weighting of One Day Internationals and Twenty20 Internationals.
Contract list:
The 21 players offered Black Caps contracts for the 2016-2017 year are:
Corey Anderson - Northern Districts
Trent Boult - Northern Districts
Doug Bracewell - Central Districts
Mark Craig - Otago
Martin Guptill - Auckland
Matt Henry - Canterbury
Tom Latham - Canterbury
Mitchell McClenaghan - Auckland
Adam Milne - Central Districts
Colin Munro - Auckland
James Neesham - Otago
Henry Nicholls - Canterbury
Luke Ronchi - Wellington
Mitchell Santner - Northern Districts
Ish Sodhi - Northern Districts
Tim Southee - Northern Districts
Ross Taylor - Central Districts
Neil Wagner - Otago
BJ Watling - Northern Districts
Kane Williamson - Northern Districts
George Worker - Central Districts