Diatoms are one of the most promising microalgae for about 25% of CO ₂ fixation. They are also known as primary producers of our Mother Earth. The main value-added products for which they have gained importance in the commercial market are due to their pigment fucoxanthin, which has high antioxidant, medicinal, therapeutic and pharmaceutical properties. Besides this, they alone provide 30% of the crude oil at the global level; therefore, their techno-economic cultivation holds promise and importance. Because of the oil abundance in them, they are a rich source of biofuel, also known as Diafuel ^T M (biofuel from diatoms). The cultivation practices used to grow diatoms, however, are not cost-effective, which raises the cost of the value-added products derived from them. The open raceway ponds and closed photobioreactors have their own pros and cons. The current chapter discusses the cultivation practices generally used to cultivate microalgae and diatoms economically. This is needed to make the biofuel to be used commercially to compensate for the requirements of renewable energy.