thumb|alt=photo of Judd Trump|upright|[[Judd Trump is the current world number one.]]
The sport of snooker has utilised a world rankings system since 1975, used to seed players on the World Snooker Tour for tournaments. Originally, rankings were published once a year at the conclusion of a season. Since 2010, however, the rankings were changed so that they would be updated after every ranking tournament. The number one ranking has been held by twelve players; Ray Reardon was the first to hold the position, and was followed by Cliff Thorburn, Steve Davis, Stephen Hendry, John Higgins, Mark Williams, Ronnie O'Sullivan, Neil Robertson, Mark Selby, Judd Trump, Ding Junhui and Mark Allen.
Hendry held the number one position for the longest time under the annual format, holding it for nine years in total. Since it changed to a rolling format in 2010, Selby has held the rank longer than anyone else.
History
thumb|alt=Hendry at the 2011 Paul Hunter Classic|upright|[[Stephen Hendry ended the season ranked at number one on nine occasions; more season finishes in the top spot than any other player.]]
The sport of professional snooker first adopted a ranking system for the 1975–76 season, which saw Ray Reardon ranked in the top position. An Order of Merit was published in the 1975/76 season to determine the seedings for events, and the first set of official rankings the following year used the same criteria. Over the next 22 seasons, five men held the first position; Reardon (1976/77 to 1980/81), Cliff Thorburn (1981/82), Reardon again for 1982/83, Steve Davis (1983/84 to 1989/90) and Stephen Hendry (1990/91 to 1997/98). From 1998/99 to 2009/10, the title was shared by Ronnie O'Sullivan (five seasons), John Higgins (three seasons) and Mark Williams (three seasons), while Hendry regained the position for the 2006/07 season. In the first 34 years of the world rankings, only seven players held the number one position. This was altered from the 2014–15 snooker season, where ranking points were based entirely on the prize money won from qualifying events. Since the introduction of the new system, Higgins, Neil Robertson, Williams, Mark Selby, Judd Trump, Ding Junhui, and O'Sullivan have all attained the number one rank. <!--, Ding is the only player to be world number one, and not have won the World Snooker Championship during their career. -->
List of players
Hendry holds the record for most seasons at number one under the traditional system, with nine seasons (1990/1991–1997/1998 and again in 2006–07). His first spell of eight consecutive seasons in this position is also a record. Under the rolling ranking format, Mark Selby holds both the total and consecutive records.
{| class="wikitable sortable plainrowheaders"
|+ Number one players
! scope=col|No.
! scope=col|Nationality
! scope=col|Player
! scope=col|From
! scope=col|To
! scope=col class="unsortable"|
|-
| style="text-align:center;" scope=row |
| || || || ||align="center"|
|-
| style="text-align:center;" scope=row |
| || || || ||align="center"|
|-
| style="text-align:center;" scope=row |
| || || || ||align="center"|
|-
| style="text-align:center;" scope=row |
| || <small>(4)</small> || || ||align="center"|
|-
| style="text-align:center;" scope=row |
| || <small>(3)</small> || || ||align="center"|
|-
| style="text-align:center;" scope=row |
| || || || ||align="center"|
|-
| style="text-align:center;" scope=row | 10
| || || || ||align="center"|
|-
| style="text-align:center;" scope=row |
| || <small>(2)</small> || || ||align="center"|
|-
| style="text-align:center;" scope=row |
| || <small>(2)</small> || || ||align="center"|
|-
| style="text-align:center;" scope=row |
| || <small>(3)</small> || || ||align="center"|
|-
| style="text-align:center;" scope=row |
| || <small>(2)</small> || || ||align="center"|
|-
| style="text-align:center;" scope=row |
| || <small>(4)</small> || || ||align="center"|
|-
| style="text-align:center;" scope=row |
| || <small>(3)</small> || || ||align="center"|
|-
| style="text-align:center;" scope=row |
| || <small>(5)</small> || || ||align="center"|
|-
| style="text-align:center;" scope=row | 11
| || || || ||align="center"|
|-
| style="text-align:center;" scope=row |
| || <small>(4)</small> || || ||align="center"|
|-
| style="text-align:center;" scope=row |
| || <small>(2)</small> || || ||align="center"|
|-
| style="text-align:center;" scope=row |
| || <small>(6)</small> || || ||align="center"|
|-
| style="text-align:center;" scope=row |
| || <small>(4)</small> || || ||align="center"|
|-
| style="text-align:center;" scope=row |
| || <small>(8)</small> || || ||align="center"|
|-
| style="text-align:center;" scope=row |
| || <small>(5)</small> || || ||align="center"|
|-
| style="text-align:center;" scope=row | 12
| || || || ||align="center"|
|-
| style="text-align:center;" scope=row |
| || <small>(5)</small> || || Present ||align="center"|
|}
Total time spent at number one
Annual format (1975–2010)
{| class="wikitable sortable"
|+Annual format
