Cells organize many of their biochemical reactions by formation and dissolution of non-membrane-bound compartments. One common mechanism for such biochemical organization is phase separation of disordered proteins to form compartments with liquid properties. These compartments can subsequently harden to form compartments with new material properties such as gels and glasses. These compartments can be described by principles elucidated from condensed-matter physics and are therefore termed biomolecular condensates. I will discuss potential roles of condensates in organization and robustness of cellular biochemistry and how they fail in neurodegenerative disease, using aggregation of TDP-43 in ALS as a model.