Think of primer as a nail polish base coat. Or, for a non-makeup reference, liken it to glue. Even though makeup will usually "stick" on its own, these products promise the ultimate in staying power. Some users even say a splurge-worthy primer can take a cheap mascara or eye shadow to a whole other level. We road-tested eight primers for eyelids, lashes and face.
Eye shadow primersThese are designed to prevent the inevitable, annoying midday creasing or fading. Be careful, though -- accidental smudges and mascara mishaps are much more difficult to remove, because these options have some serious staying power.

Laura Geller Lip & Eye Spackle
2 out of 5
Pros: Concealer-like coverage creates a smooth base for eye shadow, and the included lip primer is effective for matte color
Cons: Eyecolor showed signs of wear and tear by midday
Available at laurageller.com and Sephora, $23

Tarte Lifted Natural Eye Primer with Firmitol
5 out of 5
Pros: Eye shadow doesn't move an inch all day, plus the Firmitol is supposed to tighten eyelid skin over time
Cons: None
Available at Sephora and tartecosmetics.com, $20

Urban Decay Eyeshadow Primer Potion
4 out of 5
Pros: Keeps shadow locked to your lids; comes in both nude and a new shiny champagne color called "Sin"
Cons: Didn't hold up quite as well as Tarte's Lifted, although the difference was slight
Available at Sephora and urbandecay.com, $17

Mascara primersDesigned to up the volume and length of lashes, some primers also help to condition and separate. They're usually clear or white in color, and work best when applied to clean lashes and allowed to dry.

Clinique Lash Building Primer
4 of 5
Pros: Adds length and creates separation, plus helps curled lashes keep their shape
Cons: It can weigh down lashes if you don't let it dry before curling or applying mascara
Available at Clinique counters and clinique.com, $13

Estee Lauder Lash Primer Plus
3 of 5
Pros: Adds a bit of length, and helps lashes keep their shape when curled
Cons: Tends to cause clumpiness -- make sure you let it dry before curling or applying mascara
Available at Estee Lauder counters and esteelauder.com, $19

Shu Uemura Lash Repair
5 of 5
Pros: This thin, clear liquid helps make lashes stand out, and used twice-daily over time it'll protect and strengthen lashes
Cons: None
Available at Sephora and shuuemura-usa.com, $22

Foundation primersUneven and shiny faces get a little love from foundation primer, which is meant to combat both problems. They prep the skin for foundation and help things "stick." We tested the staying powder with loose-powder foundation and weren't impressed.

Benefit "That Gal" Face-Brightening Primer
2 of 5
Pros: Pink in color and a bit lotion-y, which might explain that "brightening" claim
Cons: Brightening look doesn't last long, and foundation doesn't either
Available at Sephora and benefitcosmetics.com, $28

Sephora "Tricks of the Trade" Anti-Shine Primer
1 of 5
Pros: This clear gel smoothes on fast, much like Smashbox's
Cons: Didn't give any noticeable longevity to foundation
Available at Sephora, $18