 For people with below-the-knee amputations, even the best prosthetics haven't been very good. Amputees often struggle to walk normally, and some have complained that it feels like their prosthetic leg is stepping in sand, even if they're walking on a sidewalk. But that's beginning to change. In the last decade or so, roboticists have taken an interest, and new bionic feet are emerging from labs. Here, we'll review some of those advances and look towards a future that promises patients unprecedented mobility. The key to making a better prosthetic foot is the ankle, which does a surprising amount of work while walking. Conventional prosthetic feet do little to replicate this important joint. More advanced energy storing feet come closer. These essentially act as springs, absorbing energy, and then releasing it to propel the foot into the next step. While the articulated versions have moving joints that are quite elaborate, there are no active components. That's where bionic feet come in. These models use pneumatic systems or motors for stabilization or propulsion. But only propulsive feet add more power than what's stored during movement and are considered state-of-the-art. We'll focus on these. There are a variety of propulsive bionic foot designs. Some store elastic energy with pneumatic tubes mimicking human anatomy. One even uses rocket-like propellant. Others channel elastic energy with springs and motors. The pneumatic systems provide the most force for their size, but getting pressurized air is costly and impractical. Amputees would have to carry air tanks and compressors on their backs while walking. The combo spring and motor feet generally take less power to operate and can be lighter and cheaper, making them popular with innovators. One such model is Arizona State's Sparky Project, which uses springs in series and can be used for running, walking on slopes, and going up and down stairs. MIT's Biome adds in springs in parallel. While not yet commercially available, roboticists at the Free University of Brussels in Belgium have also developed the AMP foot, which combines springs in series with a clutch system. All three of these state-of-the-art prostheses weigh under six pounds and are designed to replace the ankle, Achilles tendon, and calf muscles that propel the leg upward and forward during walking. Springs in series, however, reduce speed and, ultimately, peak power. There is no one perfect bionic foot. Each system has its pros and cons, and many are still in development. But for amputees, the future is bright. Fewer and fewer will ever have to wear prosthetics that feel like they're sinking in sand. Instead, they'll experience that familiar push-off on every step.