The present invention relates to amino acid sequences, compounds and polypeptides binding to tumor necrosis factor alpha ( "TNF" or "TNF-alpha" ). In particular, the present invention relates to improved heavy-chain immunoglobulin single variable domains (also referred to herein as "ISV' s" or "ISVDs" ) binding to tumor necrosis factor alpha, as well as to proteins, polypeptides and other constructs, compounds, molecules or chemical entities that comprise such ISVDs, collectively TNF binders. Other aspects, embodiments, features, uses and advantages of the invention will be clear to the skilled person based on the disclosure herein.