Level is the primary characteristic that determines a Guardian's progression and power.
In Destiny, a Guardian can reach a maximum level of 40 by gaining experience. After reaching level 40, a Guardian can increase his or her power increasing their Light. Without DLC, the player can reach a maximum level of 34. Playing the demo allows the player to reach a maximum level of 7.
In Destiny 2, a Guardian can reach a maximum level of 20 without DLC, level 25 with Curse of Osiris or Warmind and level 30 with both expansions by gaining experience. With the release of Forsaken the level cap was again raised, increasing the max level to 50.