Potions and skills offer excellent boosts to your health, but to survive multiple battles, you'll need to use them alongside a more reliable, renewable means of recovery.
That's where health globes -- floating, crimson spheres that rise from the corpses of your defeated foes -- come in. These globes are the core means of regenerating your health in Diablo III, and all other methods of healing support them. When you pick up a health globe, your health (and the health of any allies in your party) is restored by a fixed percentage depending on the type of globe you've grabbed.
Each time you slay a "regular" enemy, whether a rabid demon or a crazed cultist, there's a good chance (but not 100%) that a weak health globe will appear. Although weak globes emerge more frequently than other types of health globes, they restore the smallest percentage of your health.

When you do battle with stronger foes, like "rare" and "champion" monsters, you're likely to see medium-sized health globes emerge before these monsters are killed, as they reach certain health percentages or are stripped of their defenses. Medium globes restore a sizeable percentage of your health, but you'll need the extra boost to survive when dealing with these formidable enemies.

Major boss fights make unique use of health globes. Each boss battle includes a custom-designed means of utilizing these globes to regain health. For example, in one fight, you might have to split your attention between weakening a dangerous boss and slaying its irritating but ultimately less-dangerous minions in order to get enough health globes to stay standing. In another fight, the boss itself might drop health globes when it takes damage, or you might have to hunt for hidden caches of globes in the midst of battle.

Health globes drive Diablo III's tactical combat, making your lightning-fast decisions during battle intellectually engaging and relevant without adding needless complexity. If you're injured and attacking monsters from afar to avoid further damage, but a much-needed health globe drops, what will you do? Will you put your wand away and make a dash for it, even if doing so requires you to brave a gauntlet of Fallen, or will you cautiously hang back and wait for an opening, fighting defensively so that you aren't overwhelmed? If you're fighting a pack of enemies, can you slaughter the weaker ones quickly enough to saturate the battlefield with health globes so that you'll survive more dangerous attacks? Will you take the right risks at the right time?