What is the difference between FIR and IIR filters?

FIR (Finite Impulse Response) filters have impulse response of finite duration, implemented as weighted sum of input samples. Advantages: always stable, linear phase possible, no feedback. IIR (Infinite Impulse Response) filters have infinite-duration impulse response using feedback (recursive). Advantages: achieve sharp cutoffs with fewer coefficients (more efficient for same specification). Trade-offs: FIR needs more computation but is inherently stable; IIR is efficient but requires stability analysis and has nonlinear phase. FIR preferred for linear phase requirements; IIR for efficiency.