| # of Firms | Product Diff. | Entry/Exit | |
| Perfect Competition | Many | None | Free |
| Monopoly | One | None | Highly Restricted |
| Monopolistic Competition | Many | Significant | Free |
| Oligopoly | Few | Some | Restricted |   |
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To the left is a table showing the primary characteristics which define the four main industrial structures typically studied. As we study each type of industry, we will consider in detail the role each of these characteristics play in explaining individual firm decision making, and overall industry behavior. | ||||||||||||||||||||||||