This document summarizes key concepts in microeconomics including: - Production functions relate quantities of inputs to output - Isoquants represent combinations of inputs that produce the same output level - Marginal rate of technical substitution is the rate at which one input can be substituted for another without changing output - Economic regions of production define where isoquants have positive or negative sloping segments - Isocost lines show combinations of inputs that can be purchased with a given budget - Firms seek to produce at the optimal, least-cost combination of inputs given prices and production possibilities - Expansion paths illustrate how firms adjust input mixes as output increases at minimum cost.