This issue of MRS Bulletin explores cellular solids, materials with a porous structure composed of cells. Examples include natural materials like cork, wood, sponge, and bone, as well as engineered materials such as honeycombs and foams made from polymers, metals, ceramics, and glasses. These materials have unique properties due to their cellular structure, making them useful in various applications, including lightweight construction, energy absorption, thermal insulation, and tissue engineering. The articles in this issue discuss the fabrication, structure, properties, and applications of cellular solids, including cellular ceramics, metallic foams, and scaffolds for tissue engineering. They also cover techniques for understanding, modeling, and measuring the behavior of these materials. The structure of cellular solids has been studied for centuries, with early observations by Robert Hooke and later developments by scientists like William Thomson and Weaire and Phelan. The mechanical response of cellular solids in compression is characterized by three regimes: an initial elastic region, a stress plateau during cell collapse, and a final increase in stress during densification. Honeycomb-like cellular solids can be analyzed using structural mechanics, while foams are more complex. Local effects, such as the impact of broken struts or cell size, are best studied using numerical techniques like finite element analysis. Metallic and ceramic foams have various applications, including lightweight construction, impact absorption, and filtration. Calcium-phosphate-based foams are being developed for biomedical applications, such as bone grafts and tissue engineering scaffolds. Tissue engineering scaffolds must have interconnected pores to allow cell migration and nutrient exchange, and they must be biocompatible and degrade over time. The issue also features profiles of contributors, including Lorna J. Gibson, a leading researcher in cellular solids, and other experts in materials science and engineering. The articles highlight the importance of cellular solids in modern materials science and their potential for future applications.This issue of MRS Bulletin explores cellular solids, materials with a porous structure composed of cells. Examples include natural materials like cork, wood, sponge, and bone, as well as engineered materials such as honeycombs and foams made from polymers, metals, ceramics, and glasses. These materials have unique properties due to their cellular structure, making them useful in various applications, including lightweight construction, energy absorption, thermal insulation, and tissue engineering. The articles in this issue discuss the fabrication, structure, properties, and applications of cellular solids, including cellular ceramics, metallic foams, and scaffolds for tissue engineering. They also cover techniques for understanding, modeling, and measuring the behavior of these materials. The structure of cellular solids has been studied for centuries, with early observations by Robert Hooke and later developments by scientists like William Thomson and Weaire and Phelan. The mechanical response of cellular solids in compression is characterized by three regimes: an initial elastic region, a stress plateau during cell collapse, and a final increase in stress during densification. Honeycomb-like cellular solids can be analyzed using structural mechanics, while foams are more complex. Local effects, such as the impact of broken struts or cell size, are best studied using numerical techniques like finite element analysis. Metallic and ceramic foams have various applications, including lightweight construction, impact absorption, and filtration. Calcium-phosphate-based foams are being developed for biomedical applications, such as bone grafts and tissue engineering scaffolds. Tissue engineering scaffolds must have interconnected pores to allow cell migration and nutrient exchange, and they must be biocompatible and degrade over time. The issue also features profiles of contributors, including Lorna J. Gibson, a leading researcher in cellular solids, and other experts in materials science and engineering. The articles highlight the importance of cellular solids in modern materials science and their potential for future applications.