No, but yes is the answer to this common question.
It actually depends on the type of stretching you’re talking about, and yes, there are different types. Typically the kind of stretch before exercise people think of is the fold forward, try to touch your toes and hold briefly kind of stretch. This is passive stretching and it targets muscles. As we stretch the muscles we obviously increase their length and this improves our flexibility. Numerous published studies have shown this kind of stretching before exercise is not beneficial. Each muscle has a particular length for optimal performance; passive stretching beforehand can mess with this length potentially leading to loss of power or injury. Passive stretching after exercise is very important but before is a disservice to yourself.
Active stretching and mobilising however, are very important before exercise. Mobility refers more to the range of motion of a joint through functional patterns. Mobility utilises long holds (2-5 minutes) of poses and can involve using bands to align the joint while in the pose, and rolling. Mobility is accessing the joint and myofascia, the connective tissue that holds us in our shape and includes ligaments and tendons. Active stretching is moving the body through the ranges of motion that will be expected of it during whatever exercise you’re about to do. Think slow swinging of the arms through the paddling motion before heading out for a surf, or swinging the legs in increasing arcs before kickboxing. Active stretching is warming up the muscles and preparing them for action, it’s getting the muscle fibres sliding against each other rather than sticking together; and lubricates the joints. This decreases risk of injury and as a bonus, mobilising fascia gives you back the extra power of the elastic energy it stores.
The bottom line, mobilise before exercise and stretch after exercise. One prepares the body for action and increases range of motion, the other lengthens the muscles, helps to release them after they have been worked and increase flexibility.