This paper reviews the requirements for far-infrared astronomy in the period following the SPICA satellite in the late 2020's. We take a very long view of the state of FIR astronomy and what facilities will be required in a twenty year timeframe. We show that spatial resolution to match that of observatories operating in the optical and mid-infrared and the radio will be a necessity. Moreover this high spatial resolution must be combined with high spectral and photometric sensitivity to provide the data required to further our understanding of planetary formation mechanisms, the history of star formation through cosmic time and the feedback between active galactic nuclei and their host galaxies in controlling star formation. We review three possible conceptual mission scenarios and comment on the possibility of realising them in the coming deades.

ABSTRACT
1. INTRODUCTION
2. SCIENTIFIC PERSPECTIVE - HERSCHEL & SPICA
3. ILLUSTRATIVE CASES
    3.1. Planetary evolution
    3.2. Massive Star Formation
    3.3. AGN Feedback
    3.4. Galaxies at high redshift
4. FUTURE MISSION CONCEPTS
REFERENCES

• Bruce Swinyard(Department of Physics and Astronomy, University College London/RAL Space, STFC-Rutherford Appleton Laboratory)
• Chris Pearson(RAL Space, STFC-Rutherford Appleton Laboratory/The Open University/Oxford Astrophysics, University of Oxford)