Determinants of Supply
The determinants of supply are: technology, input prices, number of suppliers, expectations, and changes in prices of other products.
Technology allows firms to produce more at the same or at a lower cost. This decreases the marginal cost of a firm and increases the market supply.
Input prices are the costs of the factors needed to produce the good. Labor, materials, rent costs are all input prices. If input prices increase, supply will decrease because it is more costly for a given firm to supply the same amount of goods. Input prices can be pretty flighty as most prices of commodities can change over night.
If there are more suppliers, the market supply curve will shift to the right lowering price and increasing quantity. If there are less suppliers the market supply curve will shift to the left increasing price and decreasing quantity.
If expectations state that the price of a good will increase, suppliers will withhold their good until the price increases therefore decreasing supply. If expectations state that the price of a good will decrease, suppliers will try to sell off their good therefore increasing supply.

The change in complements and substitutes are important for suppliers too. If a firm produces a plethora of products, it must judge which products to produce more based on the competitive market price. If a furniture store sees an increase in price for chairs it will shift its production toward chairs and away from sofas. The same logic applies to if the housing market is booming then the firm should look to produce more of all furniture because houses and furniture are complements.

*Price changes QS