I have a character that has Inspiring Leader, and I can grant temporary hit points to my team members. We have a Druid in the group that tends to use Wild Shape frequently. When the Druid uses Wild Shape, do the Temporary Hit Points transfer over to the new form, or are they "attached" to the original form? Is there anything in the books that handle this?
You retain all temporary hit points when using wild shape.
There is nothing in the rulebook that addresses this directly, however I think we can figure this out using what we do know.
Temporary HP are not real HP because:
Temporary hit points aren’t actual hit points; they are a buffer against damage, a pool of hit points that protect you from injury.
When a Druid uses wild shape:
...you assume the beast’s hit points and Hit Dice. When you revert to your normal form, you return to the number of hit points you had before you transformed.
This would seem to imply that your hit points before wild shape are replaced with the hit points of the beast you've shaped into. But! Temporary hit points aren't actually hit points per the rule book; they are a buffer against damage.
Because temporary hit points are separate from your actual hit points, they can exceed your hit point maximum. A character can, therefore, be at full hit points and receive temporary hit points...
So even if your hit point maximum increases from wild shape, your temporary hit points remain because they are separate from your actual hit points and they can exceed your HP maximum.
Unless a feature that grants you temporary hit points has a duration, they last until they’re depleted or you finish a long rest.
Since there is nothing in wild shape that explicitly denies you your temporary hit points, they last until you have either used all of them or until you have completed a long rest.
Even better, if you still have your temporary hit points when you shape back to your original form, you will still retain them, although your "real" HP will revert to whatever level they were at before you wild shaped.
I would assume that would be the case, as PHB 198 states:
Temporary hit points aren't actual hit points; they are a buffer against damage , a pool of hit points that protect you from injury.
Also, according to PHB 67,
You retain the benefit of any features from your class, race, or other source and can use them if the new form is physically capable of doing so.
So, I believe that the temporary hit points would be retained by the druid if it uses Wild Shape.