The principles of aquaponics are introduced in this chapter. Aquaponics recycles nutrient from aquaculture effluent, producing organic vegetables. Fish, plants, and microbial community work symbiotically in aquaponics. Nitrogen is a key element in aquaponics. Understanding nitrogen transformations in aquaponics is important in system design, operation, and maintenance for the highest production. Biochemical processes provided in this chapter include nitrification, denitrification, nitrogen assimilation by plants, bacteria, etc. Concepts of modern molecular methods for aquaponics microbiome are described. Growth equations that help aquaponic growers/researchers to predict the productions of fish and plants are provided. At the end of this chapter, a design example of floating-raft aquaponics systems is shown. Aquaponics can be a future of indoor and weather independent food production (e.g., plant factory, rooftop farming); however, persuasive results from Techno Economic Analysis (TEA) and Life Cycle Assessment (LCA) are important to encourage farmers to invest in the next-generation aquaponics. Overall, we believe that this chapter can help the beginners to start growing aquaponics easily, and it will support aquaponics researchers to develop useful techniques to maximize the organic productions and nutrient use efficiencies in aquaponics.