We present an impedance engineered Josephson parametric amplifier capable of providing bandwidth beyond the traditional gain-bandwidth product. We achieve this by introducing a positive linear slope in the imaginary component of the input impedance seen by the Josephson oscillator using a λ/2 transformer. Our theoretical model predicts an extremely flat gain profile with a bandwidth enhancement proportional to the square root of amplitude gain. We experimentally demonstrate a nearly flat 20 dB gain over a 640 MHz band, along with a mean 1-dB compression point of -110 dBm and near quantum-limited noise. The results are in good agreement with our theoretical model.Josephson parametric amplifiers (JPAs) have become a crucial component of superconducting qubit 1 measurement circuitry, enabling recent studies of quantum jumps 2 , generation and detection of squeezed microwave field 3 , quantum feedback 4,5 , real-time tracking of qubit state evolution 6-8 and quantum error detection 9,10 . Although JPAs based on Josephson junctions embedded in a resonator 11-13 regularly achieve 20 dB power gain and quantum-limited noise, typical bandwidth is restricted to 10-50 MHz 11,14 , making them suitable for single qubit measurements only. The rapid progress towards multi-qubit architectures 9 for fault-tolerant quantum computing 15,16 demands an amplifier with much larger bandwidth to enable simultaneous readout of multiple qubits with minimal resources.There have been several attempts in this direction in recent years. One such attempt used a broadband impedance transformer 17 to lower the quality factor of a lumped-element Josephson oscillator which is the main component of a parametric amplifier. While the observed large bandwidth was qualitatively explained by a model consisting of a negative resistance 18 coupled to a frequency dependent impedance, no clear prescription on the design principle was provided. A different approach using Josephson non-linear transmission lines 19,20 was recently demonstrated 21,22 with nearly 4 GHz of bandwidth. However, this design requires fabrication of about 2000 nearly identical blocks of oscillator stages, demanding fairly sophisticated fabrication facilities. Multimode systems utilizing dissipative interactions have also been suggested theoretically as a route for enhancing bandwidth 23 , but have not been realized experimentally. In this Letter, we present a simple technique for enhancing the bandwidth of a JPA and beating the standard gain-bandwidth limit. It involves engineering the imaginary part of the environmental impedance: in particular, we introduce a positive linear slope in the imaginary component of the impedance shunting the JPA, while keeping the real part unchanged at the pump frequency. Our design uses a combination of a λ/4 and a λ/2 impedance transformers which are significantly easier to fabricate than a broadband impedance transformer 17 . Our theoretical model explains why the imaginary part of the impedance plays a crucial role in determining the amplifier bandw...