Thanks! This video has crucial information on the IK settings, and I learned a lot about how the pole target works. Some of the bugs that left me baffled make much more sense now.

Very informative! Thank you

I have just lost my rigging phobia the right way of things! haha. Thanks a lot.

7 years later, few more Blender versions released (3.3) and still so good! Thanks Nathan (and Mr Squeegee) for making IK basis understanding so easy.

In Blender 2.8 the X-Axis Mirror checkbox has moved. When in the armature's edit mode, open the sidebar on the right of the 3D Viewport (by default, hit the N key). Select the Tool tab. X-Axis Mirror is under Options.

Thanks so much for this, I'm an absolute beginner in blender and rigging baffled me. This video series seriously accelerated my learning process

Now I finally understand what IK is from this vedio. Indeed informative.

Tip: If your foot bone won't move and only rotates, you need to clear its parent while keeping it connected as a bone: Go into edit mode, select the foot bone, press ALT+P, and press "Clear Parent". Now you'll be able to move the foot bone and see inverse kinematics in action.(Note that "Disconnect Bone" was another option in the ALT+P menu, which implies the bones can be connected without being parented.)

Is there any way to prevent accidentally dragging the foot bone too far from the lower leg when posing? Right now I'm free to drag it far away from the leg.

Thank you so much!