How to get the envelope of all the features in a feature class in ArcMap?

Check out the Minimum Bounding Geometry tool. Specify the "ALL" for the group option to get a single feature representing the envelope of your features.

FeatureClass supports the IGeoDataset interface, which has an Extent property containing the IEnvelope used by all features

cheers brian

If you want to use the arcgisscripting Python module in 9.3x:

import arcgisscripting

gp = arcgisscripting.create(9.3)

fc = "C:/workshop/exercises/exercise1/data/stlouis_cities_geog.shp"

fcDesc = gp.describe(fc)

shpExtent = fcDesc.extent
print("Bounding Box: " + str(shpExtent.XMin) + "," + str(shpExtent.YMin) + "," +  str(shpExtent.XMax) + "," + str(shpExtent.YMax))

del fc, gp