The growing world population calls for effective means of producing food sustainably. This chapter will address some general aspects of the chemical action of products that protect crops against pest attack and the implications of these products (the so-called agrochemicals) for the environment. The main types of active ingredients used in agrochemicals and their historical development will be concisely approached. The organic synthesis of original molecules and the structural modification of natural products that are already being used in agriculture will also be briefly discussed. This discussion will show some useful and versatile tools to obtain modern molecules with advantageous biological activities in agriculture. Given that further advances in protecting crops are needed, recently developed agrochemicals that can pave the way for future research, such as nanofertilizers, nanopesticides, and nanobiosensors, will be described. Finally, this chapter will discuss current challenges in synthesizing agrochemicals, as well as cutting-edge developments in designing and synthesizing new agrochemicals, including inventing more selective and environmentally friendly active ingredients, which will help to face the ongoing challenges of weed and pest resistance.