Designed by Frederick Law Olmsted to serve as a link in the Emerald Necklace park system, the Fens gives its name to the Fenway-Kenmore neighborhood, and thereby to Fenway Park, home of the Boston Red Sox.

The Back Bay Fens is a large picturesque park that forms part of Boston's Emerald Necklace. It is essentially an ancient spot of saltwater marshland that has been surrounded by dry land, disconnected from the tides of the Atlantic Ocean, and landscaped into a park with fresh water within. The park is also known as the Fens or the Fenway. The latter term can also refer to the surrounding neighborhood.

When Boston was settled in the early 1600s the Shawmut Peninsula on which it was built was connected to Roxbury by a spit of sandy ground called "The Neck." The adjacent area of marshland to the west was a tidal flat of the Charles River. The area became malodorous with time as it became tainted with sewage from the growing settlement.

For the dual purpose of eliminating the health and aesthetic problem created by the polluted bay waters and creating new and valuable Boston real estate, a series of land reclamation projects was begun in 1820 and continued for the rest of the century. The filling of present-day Back Bay was completed by 1882. Filling reached Kenmore Square in 1890 and finished in the Fens in 1900. These projects more than doubled the size of the Shawmut Peninsula.

Olmsted’s challenge was to restore the spot of marsh which was preserved into an ecologically healthy place that could also be enjoyed as a recreation area. Combining his renowned landscaping talents with state-of-the-art sanitary engineering, he turned a foul-smelling tidal creek and swamp into "scenery of a winding, brackish creek, within wooded banks; gaining interest from the meandering course of the water."

Olmsted designed the Fens to be flushed by the tides twice daily. However, in 1910 a dam was constructed at Craigie's Bridge, closing the Charles River estuary to the ocean tides and forming a body of freshwater above the dam. Thus, the Fens became a freshwater lagoon regularly accepting storm water from the Charles River Basin.

Soon after, noted landscape architect Arthur Shurcliff, a protégé of Olmsted, added new features such as the Kelleher Rose Garden and employed the more formal landscape style popular in the 1920s and 1930s. An athletic field was also added.

In 1941, at the outbreak of United States involvement in World War II, citizens planted a Victory Garden within the Fens. While these were common in their era, the one in the Fens is now the last continually operating Victory Garden in existence and today is a much-valued community garden of flowers and vegetables.

In 1961, a group of East Fenway friends and neighbors gathered to address issues in their neighborhood. They formed a neighborhood association called The Fenway Civic Association (FCA). Volunteers took on projects to clean their streets, beautify their surroundings, and protect their residents from crime. Soon the group also started advocating for improved maintenance of parkland and other elements to ensure a safe, enjoyable neighborhood.

The gardens are now named after Richard D. Parker, one of the original organizers of the garden, who continued to garden there until his death in 1975. Because of his efforts, the Victory Gardens in the Fenway are one of only two remaining victory gardens in the U.S. dating back to World War II. During World War II, much of the food grown was sent to the armed forces, and the remaining portions were rationed. President Roosevelt stated that Americans should grow their own vegetables. The City of Boston set up 49 areas to grow gardens, including plots on Boston Common and Boston Public Garden. The Fenway Victory Gardens were established in 1942. These gardens are a central part of the Fenway community and are well known to gardeners across the country. The gardens provide the residents in the Boston neighborhoods with personal space to grow vegetables or flowers, and are private.