Potassium (K⁺) is an important macronutrient for plant growth and productivity. It fulfills important functions and it is widely included in fertilization management strategies to increase crop production. Although K⁺ is one of the most abundant elements of the earth crust, its availability to plants is usually limited leading to severe reduction in plant growth and yield. In plants, K⁺ shortage induces several responses at different levels: morphological, physiological, biochemical, and molecular. Activation of signaling cascades including reactive oxygen species, phytohormones (ethylene, auxin, and jasmonic acid), Ca²⁺, and phosphatidic acid is also triggered. In this review, we summarize the main of these adaptive responses evolved by plants to cope with K⁺ deficiency in the rhizosphere.