This lecture delves into the fundamentals of Quantum Field Theory (QFT), focusing on the classification of Conformal Field Theories (CFTs) in different dimensions and the constraints imposed by the S-matrix Bootstrap approach. The instructor explores the space of QFTs, from the classification of CFTs in 1+1 dimensions to the implications of Gravity as a path to QFT. Key topics include the Conformal Bootstrap, the holographic principle, and the AdS/CFT correspondence. Through scattering thought experiments and analytical tools, the lecture demonstrates how general principles like Lorentz invariance, causality, and unitarity shape the understanding of QFTs.