Above all, it concerns three candidates.
Leftist senator Iván Cepeda is leading in opinion polls ahead of the election. He is allied with outgoing President Gustavo Petro and has pledged to continue his efforts to achieve peace with the country's remaining guerrilla and rebel groups.
Opposing Cepeda are right-wing candidates: lawyer Abelardo de la Espriella and conservative senator Paloma Valencia.
Both have promised a tougher, more aggressive line against rebels, drug cartels and other criminals. They are both outspoken supporters of U.S. President Donald Trump.
The election is largely a vote on Petro's peace policy, which has failed to tame, among other things, the groups that refused to lay down their arms in connection with the peace agreement with the FARC guerrillas in 2016.
On the contrary, critics and experts believe that criminals and guerrillas have exploited the power vacuum and peace attempts to advance their positions. Recent years have been marked by car bombs, political assassinations, extortion and rampant drug trafficking.
At the same time, Petro's four years in power have resulted in, for example, higher employment and minimum wages - also a direction that Cepeda intends to continue.
If no candidate receives 50 percent of the vote on Sunday, which is unlikely, the top two will face off in a second round on June 21.
