Effective non-covalent radii for free and bonded atoms are widely used to describe a broad set of physicochemical phenomena, especially those where chemical bonds interplay with non-covalent interactions. In particular, the concept of van der Waals (vdW) radius goes back to 1932, starting with the idea of Mack 1 and Magat 2 to introduce a specific radius, which describes a distance an atom maintains from other atoms in the case of noncovalent interactions. There are two distinct categories of vdW radii: crystallographic and equilibrium. The first one corresponds to the closest approach of atoms in a crystal, as originally defined by Pauling and Bondi. This approach has an important limitation: when two molecules approach, their equilibrium distance is reached when the sum of all (many-body) repulsive interactions balances the attractive ones. Therefore, atoms can come closer than the sum of their respective vdW radii. On the other hand, equilibrium vdW radii are based on the distance in the vdW potential minimum between two isolated atoms. Taking this definition, Batsanov tabulated reference vdW radii values for many atoms by performing an extensive compilation of molecular systems in which these atoms are in a nearly isolated state or forming weak bonds with the environment, in addition to further data extrapolating to effectively neutral atoms. However, vdW radii defined by Batsanov are not unique since experimental structures yield a distribution of noncovalent interatomic distances. Hence, Batsanov's radii are statistical in nature. Furthermore, he does not report a unique vdW radius for the hydrogen atom. The vdW radius is a broadly useful concept when calculating or analyzing non-covalent interactions. For example, the nature of a given bond can be inferred by inspecting interatomic distances and comparing them a) Electronic mail: alexandre.tkatchenko@uni.lu to the sum of respective vdW radii . The vdW radii are also widely used in calculations of non-covalent interactions, for example, by rescaling the free (isolated) vdW radius to an effective radius that resembles an atomic size within a molecule. In practice, effective radii are employed in polarizable force fields, in the construction of the atomic cavity in solvation models, and as distance parameters for range separation damping functions in theoretical models for dispersion corrections, such as the Tkatchenko-Scheffler (TS) method, the many-body dispersion (MBD) formalism, as well as certain implementations of Grimme's DFT-D methods and the exchange-dipole moment (XDM) model. Since atomic vdW radius is an effective quantity, several definitions exist for it. For noble-gas atoms, the vdW radius is conveniently defined as half the equilibrium distance in the respective homonuclear dimers. This definition is rational since noble-gas atoms are noncovalently bonded upon interacting with each other. Other chemical elements need to be considered in molecular environments where they become effectively closed shell due to their covalent bonding within the corresponding molecule and can interact non-covalently with other atoms or molecules. However, such an approach can yield a large range of values for atomic vdW radii since it depends on the chemical environment of each atom. Hydrogen atom is the paradigmatic case for the so far ambiguous definition of the atomic vdW radius. For hydrogen, one can find different vdW radii lying between 2.1 and 3.7 Bohr. . Arguably, hydrogen is the "fruit fly" of chemistry for which a consistent definition of the vdW radius would be critical to further our understanding of vdW interactions and solvation in chemical and biological systems. However, this seems to be a perplexing and unresolved puzzle. In this Letter, we explore and discuss several ap-proaches toward a consistent determination of the vdW radius, focusing on the hydrogen atom. To estimate effective vdW radii, we employed the equilibrium distance of neutrally charged hydrogen atom systems, whose properties are largely determined through vdW interactions. Those effective vdW radii are re-scaled to free vdW radii by employing the ratio between free and effective Hirshfeld lengths of an atomic density in a molecule. In addition, our findings are compared with previously reported equilibrium values, positron-induced bonding between hydrogen anions, and system-independent methodologies such as atomic density cutoffs delineating an atomic size, vacuum virtual photon cloud caused by the hydrogen atom, as well as estimations from the atomic dipole polarizability. The latter approach is then employed to calculate the recommended set of equilibrium vdW radii of atomic elements from Hydrogen to Oganesson (1 ≤ Z ≤ 118). Let us start by reviewing a few relevant values of hydrogen vdW radii compiled from prior literature, collected in Figure . Overall, different methodologies provide a wide range of values, with some notable variations even within each category. Regarding the crystallographic vdW radius, the original value by is the most commonly accepted, as has been confirmed by recent revisions. For molecular systems, Batsanov reported three possible averaged values for the equilibrium vdW radii for many atoms: R e , as a fitting parameter in a vdW potential molecular mechanics model, 8 R G determined experimentally from the structure of molecules containing noble gas atoms (Rg-M or Rg-M 2 ), and R 0 as a radius of elements in MX n (X: halogens) molecules reduced to zero charge on the metal atom. Batsanov did not recommend a particular value for the vdW radius of atomic hydrogen. The atomic probes also display a wide range of values depending on the target system, the probe, and the nature of their bonding. Finally, atomic sizes from a fixed electron-density contour value are intrinsically dependent on the choice of the density cutoff. We will revisit the last three definitions in what follows.