I. INTRODUCTION  
II. COSMOLOGICAL OBSERVABLES ON ULTRA-LARGE SCALES  
A. Relativistic effects in large-scale structure  
B. Primordial non-Gaussianity  
III. FORECASTING FORMALISM  
A. Fisher matrix with multiple tracers  
B. Why multi-tracer surveys beat cosmic variance  
IV. OPTICAL AND NEAR-INFRARED EXPERIMENTS  
A. Photometric redshift surveys  
B. Forecasts  
V. RADIO EXPERIMENTS  
A. Cosmological radio surveys  
B. Forecasts  
VI. SYNERGIES  
VII. DISCUSSION