CONSPECTUS: Soft materials, which are optically transparent and exhibit high mechanical performance, will be key materials in important research areas in our future lives, such as highly advanced medicine, soft robotics, and wearable displays. When soft materials are transparent, objects underneath the soft material can be observed by the naked eye. Additionally, because they allow light to pass through, such materials can be used in optical applications such as lenses and displays. Therefore, transparent materials make it possible to transmit light information. Such transparent soft materials have been widely used in our daily life, but their applications will be directed to higher value-added products in the future.One example of a great transparent and flexible soft material is transparent silicone rubber, but even this material is not without drawbacks. Silicone rubber has the property of not adhering to most materials. This feature can be an advantage, but it can also be a disadvantage in some applications. Moreover, its tensile strength, tear strength, and friction resistance are not always strong. The ability to develop transparent soft materials whose surface and mechanical properties differ from those of silicone rubber will lead to the development of various technologies that will enrich our lives. By use of colloid-sized molecules and materials as building blocks to form soft materials, the properties and functions of the resulting soft materials are expected to reflect those of the building blocks. In addition, if the soft material is formed such that the building blocks have a characteristic order, the physical properties derived from the ordered structure can be manifested in the soft material. If the size of the order is as large as the wavelength of light, it is possible to develop materials that can manipulate light. The authors have been working for many years on soft materials in which building blocks of various colloidal sizes are obtained in an ordered state. As a result, we have reported that we can obtain soft materials that are optically transparent and exhibit a variety of mechanical properties. In this Account, we introduce our various works on optically transparent soft materials consisting of colloidal building blocks that exhibit high mechanical performance. To help you understand our research, a basic description of the optical transparency of the materials and the mechanical properties of the materials is given in the Supporting Information, which you are invited to read if necessary.