8. UNANSWERED QUESTIONS

I conclude with a list of questions I think we need to address before claiming to understand the nature of infrared emission from normal galaxies.

• Is there a fundamental difference between normal and ``starburst'' galaxies?

• What is the best way to separate ``cirrus'' emission from emission from star-forming regions?

• Do measurements of visible H II regions provide a reliable guide to the current star formation rate?

• Is the far-infrared optical depth in spiral galaxy disks large enough to produce self-absorption at high inclination?

• Does the radio emission come from supernova remnants or from cosmic rays in the interstellar medium?

• What is going on in early-type barred galaxy nuclei?

• Is there star formation in S0 galaxies?

• Do star formation conditions in the central regions of spiral galaxies resemble those in the disks?