The most important point for XHV technology is control of hydrogen emitted from the bulk. If we generate XHV, which is denoted by a hydrogen equivalent pressure below P=10@super -10@(H@sub 2@)Pa in a vacuum chamber, from the equation P=Q/S at the ultimate pressure, the limiting level of total outgassing should be below Q=PS=~10@super -11@Pa(H@sub 2@)m@super 3@/s when the pumping speed is e.g. S=~0.1m@super 3@/s. Here, we need three technologies for XHV, a minimum amount of a chamber, a pump and a gauge, in order to check the generated vacuum. However, if there is a large hydrogen outgassing from any component, the ultimate pressure is limited by that total value. That is, Q@sub total@(material)= Q@sub c@(chamber)+Q@sub g@(gauge)+Q@sub p@(pump) In the case of the chamber, a surface area of A=~0.5m@super 2@ is typical for a laboratory, therefore, the hydrogen outgassing rate from the material should be below q=Q/A=~2×10@super -11@Pa(H@sub 2@)m/s. To meet this situation, we have obtained an outgassing of Q=~10@super -12@Pa(H@sub 2@)m@super 3@/s for a hot-cathode ionization gauge and the extremely low outgassing rate of q=~10@super -14@Pa(H@sub 2@)m/s in the material of a 0.2% beryllium copper alloy. Therefore, we can easily obtain XHV in a laboratory using a pump of only a few liters/second. At the session, the process of development up to the present will be reviewed with the following program: (1) the importance of low emissivity material, (2) the unavailability of cold emitters for a gauge, (3) the concept of the heated-grid gauge/RGA, (4) the importance of copper alloy materials, (5) a comparison of recently-published ultra-low hydrogen outgassing materials, and (6) my conclusion for hydrogen outgassing reduction.