According to Marx, the source of value is labor. This means that the value of a product is determined by the amount of labor that went into producing it. In Marx`s view, labor is the only factor that creates value, while capital and land themselves do not contribute to the creation of value. This idea is known as the labor theory of value and is a central concept in Marx`s critique of capitalism. Marx argued that labor is exploited under capitalism, with workers not receiving the full value of their labor because profit is taken by the capitalist class. It is important to note that Marx`s concept of value is different from the concept of price, which takes into account factors such as supply and demand in the market.