On the surface they look fairly similar.
USPSA was formed in 1984 and was originally defense-oriented.
However, it has definitely grown into more of a technical/speed-based sport.
IDPA was developed years later, in 1996, and was and still is mostly defensive/tactically oriented.
While they are comparable in many ways, Id call them cousins before Id call them brothers.
If you want the detailed rules, go check out the super-engaging online rulebooks for USPSAhereand IDPAhere!
USPSA allows for more firearm modifications in some forms.
USPSA also offers divisions that are not found in IDPA at all (such as Open Division).
IDPA also requires some form of cover garment,like a vestor large overshirt.
IDPA, by contrast, will be much more structured with a more specific way to engage the targets.
IDPA will challenge you to complete the course in a more defined tactical manner, in the fastest time.
Both are going to have strategies as to how to complete the race the fastest.
This analogy might be an over-simplification, but it captures the spirit of each organization.
Until then, stay safe, stay on target, and get out and shoot!
