Magnetostriction measurements from 77 K to room temperature on oriented (100) and (110) disk samples of Fe_93.9Be_6.1 and Fe_88.7Be_11.3 reveal substantial increases in λ₁₀₀compared to iron. For the 11.3% alloy, λ₁₀₀=110 ppm, a sixfold increase above that of α-Fe. For the 6.1% alloy, λ₁₀₀=81 ppm, ∼40% and ∼170% greater than λ₁₀₀ of comparable Fe–Ga and Fe–Al alloys, respectively, for H=15 kOe. Large differences exist between the values of λ₁₀₀ and λ₁₁₁ (λ₁₀₀>0, λ₁₁₁<0) and their temperature dependencies. Elastic constants, c₁₁, c₁₂, and c₄₄, from 4 to 300 K were obtained on the same Fe–Be alloys. From these measurements, the magnetoelastic energy coefficients b₁ and b₂ were calculated. While the magnitudes of the magnetostrictions λ₁₀₀ and λ₁₁₁ are widely different, the magnitudes of b₁ and b₂ are within a factor of 2. The Fe–Be alloys are highly anisotropic magnetostrictively, elastically, and magnetoelastically. For Fe_88.7Be_11.3 at room temperature λ₁₀₀/λ₁₁₁, 2c₄₄/(c₁₁−c₁₂), and b₁/b₂ are −6.6, 3.55, and −1.86, respectively.