We're moving into thinking about how markets work and in order to do that, in the back of our head we have to realize that markets, I can show you, you could make 100 percent accurate depiction of what the costs are to produce some product in some industry, say the widget industry. So you know exactly what firm's cost curves look like in the widget industry. Now, what price do you think will be the outcome in the widget industry? Well, we still need more information. Even if I tell you what the demand curve for widgets looks like accurately and even if you know a completely accurate depiction of what the cost curves look like, you got to have to realize that you can expect that prices will be different if there are 10,000 firms in the widget industry, versus one firm in the widget industry. One firm, we'll call a monopoly, is going to behave a lot differently than if there's 10,000 competitors at each other's throat trying to get their products out into the consumers hands. So we have to think about something here that economists call market structure. So we want to think about how to characterize market structure. So market structure, really to put it differently, market structure is really thinking about the competitiveness of an industry and in order for us to think about this, we're going to think about what economists like to think of as a number line. So I'm going to draw for you a number line here. I'm going to actually just draw horizontal line. This number line will measure the number of firms in an industry. Over here on the left-hand side, we got one. In this, you may only have firm. Now, we call this a monopoly. We will devote several videos to thinking about how a monopolist behaves. A monopoly situation is when there's one firm and only one firm selling its product. At the other end, way out here, we'll say there are N firms, where N is very large. We're going to call that competition, a competitive market and we'll have lots of videos about that. In the middle here, where we have two, or three, or four, or some level, this gray zone goes by the name of oligopoly. Oligopoly means, it's Greek for competition amongst the few. So an oligopoly is a situation where there's not a monopoly but there's also not a lot of people out there competing for it. So think about the number of firms selling, let's say, mid-size automobiles in the United States. Well, there's a handful of firms selling mid-size automobiles. There's a couple firms that are giants of that industry. So you have Toyota with its Camry and Honda with it's Accord. Those are like the two big deals in the mid-size automobile market and these two companies know each other. Not only do they know each other, they know a lot about each other's behavior, they know a lot how each other responds to external events. So that type of outcome is going to have sometimes very interesting characteristics. But what we're going to do is we're going to start with the easy ones. So when we go into market structure, we're going to begin our foray in the market structure by thinking about situations where there's just tons of players out there and we're going to work out what the equilibrium will look like. We can do that, we can figure out what the equilibrium will be when you have lots and lots and lots of players. We have to put some restrictive assumptions on, what type of product are they selling? How is the information structure in the market? Are there government regulations in the market? All these things will change the outcome. But we need to start by figuring out how you would take a known cost technology and a known market demand curve, and then say 100,000 producers out there, what's going to be the outcome? Then we're going to go clear to the other end and pick this polar example. So we're going to do the poles to begin with, the polar example of monopoly. The monopoly situation will be, as we said, when there's really only one firm in this industry. Then after we get all that stuff done, we'll turn to what is arguably the more relevant situation. There are not that many competitive industries and there's not that many monopolistic industries. But there's quite a few industries out there that have a small number of players who really know a lot about each other. We're going to figure out how to solve the oligopoly problem. Essentially, we're going to turn to some work that the mathematicians have helped us to understand called Game Theory. We'll figure out how it is that street people who have strategic interests will compete against each other. Thanks.