This paper reviews the status of chemical vapor deposition (CVD) of diamond. The CVD process has made enormous steps forward contrasted to high pressure/high temperature (HP/HT) synthesis. Fabrication of coatings and free standing diamond plates exceeding 10 cm has become a reality. But perseverance is necessary in solving many difficult problems, which have created barriers in widening diamond applications. As CVD and HP/HT research proceeded, a challenge came from suggestions that "harder than diamond" beta -C3N4 material can be predicted from first principles calculations. A more recent claim "diamond hardness achieved" considers nanograin hardening in composite material films TiN/SiNx. These results and suggestions have kept a high level of research activity around hard materials and at the same time disclosed difficulties in understanding and measuring hardness.