Introductory Text for GAM I'm looking for a text to help someone who uses GLMs in practice become familiar/comfortable with GAMs.  Online or physical textbook would be fine.  I am approaching this as a practitioner, so I would prefer practical to theoretical, but I'm confident I have the background to digest a more theoretical text if it happens to be particularly worthwhile.
I also use R, almost exclusively.  If you happen to know of some R oriented texts/tutorials that'd be really appreciated. 
 A: Buja et al., (1989) give a nice overview of GAMs in the context of other additive nonparametric smoothing models. If I recall correctly, most of their examples can be easily done in R using existing packages.
Buja, A., Hastie, T., and Tibshirani, R. (1989). Linear Smoothers and Additive Models. The Annals of Statistics, 17(2):453–510.
A: I thought Michael Clark's overview is excellent:
https://m-clark.github.io/generalized-additive-models/
A great short (very short) introduction to get you started.
A: Hastie & Tibshirani's original textbook is still a great read IMO: Hastie, T. & Tibshirani, R. (1990) Generalized Additive Models, Chapman & Hall. I personally found it much easier to follow than Simon Wood's text, even if the latter is more up-to-date.
A: I came across this introductory video on GAM that I thought was helpful and easy to follow:
https://www.youtube.com/watch?v=nXDYapfalt4
A: Not a text but I found this to be a great resource for GAMs using R: https://noamross.github.io/gams-in-r-course/
It leads you through the nature of fitting a GAM without getting into the maths involved.
A: See chapter 3 in "Mixed effects models and extensions in ecology with R. 
A Zuur, EN Ieno, N Walker, AA Saveliev, GM Smith"
Ch3 provides a really basic intro to GAM in both the GAM and MGCV packages. In further chapters the book covers a lot of the things you might do with GAM and goes into  GAMM, and zero-inflated GAM. 
Its a great intro and also helpful for advanced applications. 
