The main reading is a set of lecture notes that will be provided on Canvas at the start of the semester.
It is not necessary to buy a textbook, but you may find it useful to get an alternative exposition of the material, additional problems, etc.
Recommended textbook:
Stock and Watson: Introduction to Econometrics, 4th edition
Alternative textbook:
Wooldridge, J.: Introductory Econometrics, 7th edition (slightly more technical than Stock and Watson but overall similar)
If time: one or two academic articles on business topics.