In a matter of decades, a spectacular cold-water paradise thirty million years in the making is succumbing to warming oceans. Kelp forests are largely out of sight, hidden under the ocean's surface, yet they are one of Earth's most wonderous and underappreciated marine habitats. It's an ethereal light-infused realm of sharks, otters, eels, sea stars, crabs, rockfish, and myriad other species vital to a functioning ocean and the countless coastal communities that make their living from the sea. Unlike coral reefs, whose similar plight plays out in tropical waters highly visible to vacationing tourists, kelp forests thrive along cold-water coastlines far from tourist centers. What will it take to stop the decline before these underwater playgrounds bursting with colorful life become vast fields of lifeless urchin barrens? For readers who know kelp only as tangles on the ocean surface or smelly mounds of seaweed littering beaches, Forest of the Sea reveals a thriving three-dimensional underwater world of color and beauty whose loss if allowed to happen will reverberate in unimaginable ways for both nature and humans. Author David Helvarg, a veteran journalist and accomplished scuba diver, takes us on a memorable journey beneath the waves through kelp's natural and human history, the billions of dollars of products and services it contributes to our global economy, the unwitting human activities that threaten its survival, and the hopeful movements around the world to restore kelp habitat. Helvarg introduces us to Indigenous leaders promoting sea otter reintroduction, out-of-work urchin fisherman, documentary filmmakers, and ocean scientists all working in an unlikely collaboration to restore and protect kelp forests while promoting a growing range of uses for food, medicine, and energy. Forest of the Sea is the first book to document what is at stake if we lose these irreplaceable marine jewels, helping readers to understand how these natural systems might adapt and survive.