Sidney and Shelley belong to two different periods of literature. Sidney is a Renaissance model, while Shelly is a Romantic one. The two critics reveal almost certain points of similarities and differences in their understanding of the concept of poetry. Therefore, the paper aims at shedding light on the two concepts. Defending poetry against contemporary attack was the motive shared by both Sidney and Shelley in their essays. Sidney's defence was an answer to the puritan fanatics of the 16th century led by Stephen Lasson in his "School of Abuse". The main attack on poetry was on the ground of its immortality. As for Shelley, his retort was to the 19th century thinkers understanding poetry on the ground of its worthlessness. Not only were the motives the same with the two writers but the major arguments are also quite similar. One may note a number of close parallels especially in the areas .