Under the New World Economy, material needs and money no longer existed and humanity had grown out of its infancy. People were no longer obsessed with the accumulation of things, effectively eliminating hunger and the want for possessions. The challenge and driving force then were to self-improvement, self-enrichment and the betterment of all humanity. (Star Trek IV: The Voyage Home, TNG: "The Neutral Zone", "The Price", "Time's Arrow, Part II", Star Trek: First Contact)
However, the Federation continued to deal with other cultures which had money-based economies. The Ferengi in particular were scornful of the Federation's economic system:
"I'm Human, I don't have any money."
"It's not my fault that your species decided to abandon currency-based economics in favor of some philosophy of self-enhancement."
"Hey, watch it. There's nothing wrong with our philosophy. We work to better ourselves and the rest of Humanity."
"What does that mean exactly?"
"It means... it means we don't need money!"