  The mid-infrared period-luminosity (P-L) relation for Cepheids will be
important in the JWST era, as it holds the promise of deriving the Hubble
constant within 2% accuracy. We present the synthetic P-L and period-color
(P-C) relations, derived from a series of stellar pulsation models with varying
helium and metallicity abundance, in the Spitzer IRAC bands. Selected synthetic
P-L and P-C relations were compared to the empirical relations derived from
Galactic and Large Magellanic Cloud Cepheids. We also present the empirical P-L
relations based on the latest distance measurements using infrared surface
brightness techniques.
