It is known that Wilson and 't Hooft loops are a powerful tool for
After a brief review of electric and magnetic screenings, I will talk about the behavior of the
Wilson and 't Hooft loops and compute the confinement index in a wide class of N=1
supersymmetric gauge theories. Also I will show that such behaviors are consistent
with the theta-angle periodicity and with the factorization property
of Seiberg-Witten curves.